Признаки графа институционального владения по данным 13F

# 07_institutional_holdings_graph.py


```py
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# %% [markdown]
# # Institutional Holdings Graph: Point-in-Time 13F Features
#
# **Docker image**: `ml4t`
#
# **Chapter 22: RAG for Financial Research** (Section 22.8)
#
# This notebook constructs a bipartite institution-stock graph from 13F
# holdings and derives co-ownership similarity, crowding, and institutional
# ownership-change descriptors for downstream research.
#
# **Learning Objectives**:
# - Build a normalized institution-by-stock ownership matrix and translate it
#   into stock-stock cosine similarity
# - Engineer cross-sectional ownership-breadth and ownership-change features
# - Identify portfolio overlap and strategy clusters via institution-institution
#   similarity
# - Inspect the stock-level features that downstream GNN pipelines consume
#   (the canonical downloader is the producer; Chapter 23 is the consumer)
#
# **Book Reference**: Chapter 22, Section 22.8 (Applications)
#
# **Prerequisites**: The raw 13F holdings are produced by the canonical
# downloader at `data/equities/positioning/13f_download.py`; run it once
# before this notebook (or see `data/equities/fundamentals/README.md`).
# The download mechanics (SEC EDGAR submissions API, XML information tables)
# are covered in Chapter 4, NB 05.
#
# ## What 13F Data Exposes
#
# - **Delayed disclosure**: reporting-quarter positions become observable only
#   on their SEC filing dates
# - **Manager-level positions**: Quarter-end long equity holdings by reporting
#   institution, joinable to price data for downstream feature studies
# - **Crowding descriptors**: Breadth and concentration summarize how disclosed
#   ownership is distributed; liquidation pressure is not measured here
# - **Co-ownership structure**: Stocks sharing institutional holders form a
#   bipartite graph usable for similarity and clustering analysis

# %% [markdown]
# ## Setup
#
# These parameters set the institution universe and the filing horizon. The raw
# data is already on disk; this notebook loads it through the canonical loader
# and narrows it.

# %%
"""Institutional Holdings Graph - point-in-time 13F ownership descriptors."""

import numpy as np
import plotly.graph_objects as go
import polars as pl
from IPython.display import display
from polars.testing import assert_frame_equal

from data import load_13f_edges, load_13f_stock_features, load_institutional_holdings_13f
from utils.style import COLORS, show_plotly_with_alt

# %% [markdown]
# The institution universe is a list of CIKs and the display name comes from
# the filing, not from this file. The CIK is the identity, and a hand-written
# label that disagrees with the filer renames a manager in every table
# downstream. This notebook carried one: 0001450144 was written as "Two Sigma
# Investments", and that CIK files as TWO SIGMA SECURITIES, LLC - the
# market-making entity, a different book from Two Sigma Investments LP.
#
# Extend the list to widen the analysis; rows for any other CIK in the artifact
# are dropped.

# %% tags=["parameters"]
NUM_QUARTERS = 4
MAX_INSTITUTIONS = 0

SELECTED_CIKS = [
    "0001067983",
    "0001350694",
    "0001037389",
    "0001450144",
    "0001009207",
    "0001167557",
    "0001423053",
    "0001273087",
    "0001603466",
    "0001167483",
]

# %%
if MAX_INSTITUTIONS > 0:
    SELECTED_CIKS = SELECTED_CIKS[:MAX_INSTITUTIONS]

print(f"Institution filter: {len(SELECTED_CIKS)}")
print(f"Quarters to retain: {NUM_QUARTERS}")

# %% [markdown]
# ## Part 1: Load Holdings Data
#
# `data/equities/positioning/13f_download.py` fetches 13F-HR filings from SEC
# EDGAR, parses each information table, and writes a single
# `institutional_holdings.parquet` artifact to
# `$ML4T_DATA_PATH/equities/positioning/13f/`. We read that artifact
# directly and narrow it to the institutions and quarters of interest.
#
# If the file is missing, the loader raises `DataNotFoundError` with a pointer
# to the downloader and its README.
#
# The institution count and the quarter window set the graph's density, and
# every descriptor below inherits them. Ten managers is a small universe, and
# Part 3 shows what that does to a similarity computed over it.

# %%
holdings_df = load_institutional_holdings_13f()
required_provenance = {"report_date", "put_call"}
missing_provenance = required_provenance - set(holdings_df.columns)
if missing_provenance:
    raise ValueError(
        "The canonical 13F artifact lacks required SEC provenance: "
        f"{sorted(missing_provenance)}. Regenerate it with the canonical downloader."
    )
if holdings_df.schema["report_date"] != pl.Date:
    raise TypeError("Canonical 13F report_date must use the Polars Date type.")


# %% [markdown]
# Whether a manager filed for a quarter, and when that quarter became public,
# are questions about what was *disclosed* rather than about what enters the
# graph. The producer counts any disclosed row as evidence a manager filed, so
# both are answered from the selected holdings before the option filter below:
# a manager disclosing options only has still filed. Reading coverage off the
# filtered frame would make this notebook reject a quarter the producer used,
# and the parity assertion at the end would compare two different quarters.

# %%
holdings_df = holdings_df.filter(pl.col("cik").is_in(SELECTED_CIKS))
disclosed_df = holdings_df
option_rows = holdings_df.filter(
    pl.col("put_call").fill_null("").cast(pl.Utf8).str.strip_chars() != ""
).height
holdings_df = holdings_df.filter(
    pl.col("put_call").fill_null("").cast(pl.Utf8).str.strip_chars() == ""
)
print(f"Excluded {option_rows:,} put/call rows; retained long-equity rows only.")

if holdings_df["filing_date"].min().isoformat() < "2023-01-03":
    raise ValueError("Pre-2023 13F values require a thousands-to-dollars conversion.")

# The producer retains its legacy `value_thousands` field name, but SEC filings
# after 2023-01-03 report market value in dollars. SEC reportDate supplies the
# authoritative quarter identity; filing date remains the availability time.
holdings_df = holdings_df.with_columns(
    pl.col("value_thousands").cast(pl.Float64).alias("reported_value_usd"),
    pl.col("report_date").alias("report_period"),
)

# %% [markdown]
# A reporting quarter becomes available only once the last included manager has
# filed for it. Duplicate CIK/CUSIP rows inside one information table are
# summed rather than picked from positionally.

# %%
quarter_availability = (
    disclosed_df.with_columns(pl.col("report_date").alias("report_period"))
    .group_by("report_period")
    .agg(pl.col("filing_date").max().alias("timestamp"))
)

# %% [markdown]
# Canonicalize each CUSIP's issuer label by the largest disclosed value in that
# reporting period, with a lexical tie-break, so a manager's spacing or
# abbreviation does not decide how a company is named below.
#
# A quarter then enters the graph only once every covered manager has filed for
# it. Filings are due 45 days after quarter end, so inside that window the
# newest quarter holds the early filers only, and their peers' absence would
# read as a mass exit rather than as missing coverage. The downloader applies
# the same rule, which is what keeps the reconstruction at the end of this
# notebook equal to its artifacts.

# %%
issuer_names = (
    holdings_df.group_by(["cusip", "report_period", "issuer"])
    .agg(pl.col("reported_value_usd").sum().alias("issuer_value_usd"))
    .sort(
        ["cusip", "report_period", "issuer_value_usd", "issuer"],
        descending=[False, False, True, False],
    )
    .unique(subset=["cusip", "report_period"], keep="first", maintain_order=True)
    .select("cusip", "report_period", pl.col("issuer").alias("issuer"))
)
positions_df = (
    holdings_df.group_by(["cik", "cusip", "report_period"])
    .agg(
        pl.col("company_name").sort().first().alias("company_name"),
        pl.col("reported_value_usd").sum().alias("reported_value_usd"),
        pl.col("shares").sum().alias("shares"),
    )
    .filter(pl.col("reported_value_usd") > 0)
    .join(issuer_names, on=["cusip", "report_period"], how="left")
    .join(quarter_availability, on="report_period", how="left")
)

covered_ciks = disclosed_df["cik"].n_unique()
complete_periods = (
    disclosed_df.with_columns(pl.col("report_date").alias("report_period"))
    .group_by("report_period")
    .agg(pl.col("cik").n_unique().alias("n_ciks"))
    .filter(pl.col("n_ciks") == covered_ciks)["report_period"]
    .to_list()
)
if not complete_periods:
    raise ValueError(
        f"No reporting quarter is covered by all {covered_ciks} institutions in the "
        "artifact, so no graph can be built without treating missing filers as exits."
    )
partial_periods = sorted(
    set(positions_df["report_period"].unique().to_list()) - set(complete_periods)
)
if partial_periods:
    print(
        f"Excluded {len(partial_periods)} partially filed quarter(s): "
        f"{', '.join(str(p) for p in partial_periods)}"
    )
positions_df = positions_df.filter(pl.col("report_period").is_in(complete_periods))
# Held before NUM_QUARTERS narrows the display: the change table is computed
# over the artifact's last two complete quarters, as the producer does.
complete_positions_df = positions_df

if NUM_QUARTERS > 0:
    recent_periods = (
        positions_df["report_period"].unique().sort(descending=True).head(NUM_QUARTERS).to_list()
    )
    positions_df = positions_df.filter(pl.col("report_period").is_in(recent_periods))

assert (
    positions_df.select(pl.struct(["cik", "cusip", "report_period"]).is_duplicated().any()).item()
    is False
)

print(
    f"\nTotal: {len(positions_df):,} aggregated positions across "
    f"{positions_df['report_period'].n_unique()} reporting quarters and "
    f"{positions_df['cik'].n_unique()} institutions"
)

# %% [markdown]
# Each row is a position disclosed as of a quarter end, not evidence about
# what was held between quarter ends. A manager can open and close a position
# inside a quarter and disclose neither.

# %% [markdown]
# ## Part 2: Bipartite Graph Construction
#
# The fundamental structure is an **Institution -> Stock** edge list with value
# and share weights that can be reused for graph analytics and feature export.

# %%
# Get most recent snapshot per institution-stock pair
if len(positions_df) > 0:
    latest_period = positions_df["report_period"].max()
    latest_holdings = positions_df.filter(pl.col("report_period") == latest_period)

    n_inst = latest_holdings["cik"].n_unique()
    n_stocks = latest_holdings["cusip"].n_unique()
    n_edges = len(latest_holdings)

    print("=== Bipartite Graph Structure ===")
    print(f"Institution nodes: {n_inst}")
    print(f"Stock nodes: {n_stocks}")
    print(f"Edges (holdings): {n_edges:,}")
    print(f"Density: {n_edges / (n_inst * n_stocks):.4f}")
    print(f"Avg holdings per institution: {n_edges / n_inst:.0f}")
    print(f"Avg institutions per stock: {n_edges / n_stocks:.2f}")
else:
    latest_holdings = positions_df

# %% [markdown]
# ## Part 3: Co-Ownership Analysis
#
# **Key insight**: Common disclosed owners create a stock-stock similarity graph useful for:
# - Portfolio diversification (avoid co-owned stocks)
# - Factor construction (co-ownership as a factor)
# - Risk management (crowding detection)
#
# Read the density above before the similarities below. It is the share of
# possible institution-stock edges that exist, and at ten managers each holding
# thousands of names it is not small.


# %%
def build_ownership_matrix(holdings: pl.DataFrame) -> tuple[np.ndarray, list[str]]:
    """Build an institution-by-stock matrix weighted by reported position value."""
    stocks = sorted(holdings["cusip"].unique().to_list())
    institutions = sorted(holdings["cik"].unique().to_list())
    stock_idx = {s: i for i, s in enumerate(stocks)}
    inst_idx = {c: i for i, c in enumerate(institutions)}

    ownership = np.zeros((len(institutions), len(stocks)), dtype=np.float32)
    for row in holdings.iter_rows(named=True):
        ownership[inst_idx[row["cik"]], stock_idx[row["cusip"]]] = row["reported_value_usd"]

    row_sums = ownership.sum(axis=1, keepdims=True)
    row_sums[row_sums == 0] = 1
    return ownership / row_sums, stocks


# %% [markdown]
# ### Stock co-ownership similarity
#
# Convert the normalized institution-by-stock matrix into a stock-by-stock
# cosine-similarity matrix for crowding and overlap analysis.
#


# %%
def compute_coownership_matrix(holdings: pl.DataFrame) -> tuple[np.ndarray, list[str]]:
    """Compute the stock-level co-ownership similarity matrix."""
    ownership_norm, stocks = build_ownership_matrix(holdings)
    coown = ownership_norm.T @ ownership_norm
    diag = np.sqrt(np.diag(coown))
    diag[diag == 0] = 1
    similarity = coown / np.outer(diag, diag)
    return similarity, stocks


# %%
if len(latest_holdings) > 0:
    coown_matrix, stock_list = compute_coownership_matrix(latest_holdings)
    np.fill_diagonal(coown_matrix, 0)
    row_idx, col_idx = np.triu_indices_from(coown_matrix, k=1)
    pair_values = coown_matrix[row_idx, col_idx]

    ownership_norm, _ = build_ownership_matrix(latest_holdings)
    holder_counts = (ownership_norm > 0).sum(axis=0)

    print("=== Co-Ownership Matrix ===")
    print(f"Shape: {coown_matrix.shape} over {len(pair_values):,} distinct stock pairs")
    print(f"Pairs sharing no holder at all: {(pair_values == 0).mean():.1%}")
    print(f"Pairs below 1% similarity:      {(pair_values < 0.01).mean():.1%}")
    print(f"Pairs at or above 0.999:        {(pair_values >= 0.999).mean():.1%}")

# %% [markdown]
# ### Why so many pairs sit at the maximum
#
# The similarity is a cosine between two columns of a matrix with one row per
# institution, and there are ten institutions. A stock held by exactly one of
# them is a vector pointing along one axis, so any two stocks held by the same
# single institution have a cosine of exactly 1 - not because they are alike in
# any way an investor would recognise, but because there is one dimension of
# evidence about each of them and it happens to be the same one.
#
# The count below is what that does to the top of the ranking.

# %%
if len(latest_holdings) > 0:
    saturated = pair_values >= 0.999
    single_holder_share = float((holder_counts == 1).mean())
    if saturated.any():
        endpoints = np.concatenate(
            [holder_counts[row_idx[saturated]], holder_counts[col_idx[saturated]]]
        )
        one_holder_endpoints = float((endpoints == 1).mean())
        print(
            f"Stocks held by exactly one institution: {(holder_counts == 1).sum():,} of "
            f"{len(holder_counts):,} ({single_holder_share:.0%})"
        )
        print(f"Pairs at similarity >= 0.999: {int(saturated.sum()):,}")
        print(f"  of their endpoints, {one_holder_endpoints:.0%} are single-holder stocks")
        print(f"  median holders per endpoint: {int(np.median(endpoints))}")

# %% [markdown]
# So "the highest co-ownership pair" is not a fact about two securities. It is
# one arbitrary member of a very large tie, and the notebook used to print it
# to three decimal places as though it had found something.
#
# The obvious repair is to require a minimum number of holders. The sweep below
# measures how much that buys, and it also shows what it does not fix.

# %%
if len(latest_holdings) > 0:
    floor_rows = []
    for floor in (1, 2, 3, 5, 8):
        eligible = np.flatnonzero(holder_counts >= floor)
        if len(eligible) < 2:
            continue
        block = coown_matrix[np.ix_(eligible, eligible)]
        upper = block[np.triu_indices_from(block, k=1)]
        columns = ownership_norm[:, eligible]
        top_share = columns.max(axis=0) / columns.sum(axis=0)
        floor_rows.append(
            {
                "min_holders": floor,
                "stocks": len(eligible),
                "pairs_at_or_above_0999_pct": round(100 * float((upper >= 0.999).mean()), 4),
                "max_similarity": round(float(upper.max()), 4),
                "median_top_holder_share": round(float(np.median(top_share)), 2),
            }
        )
    display(pl.DataFrame(floor_rows))

# %% [markdown]
# Requiring more holders thins the saturation sharply - the share of pairs at
# the top of the scale falls by orders of magnitude across those rows - and it
# does not reach zero until the floor is high enough to leave very few stocks.
# The last column says why.
#
# A cosine is dominated by the largest component, not by the count of non-zero
# ones. A stock held by five managers where one of them holds most of the
# position is, for this purpose, almost a one-dimensional vector, and two such
# stocks sharing that dominant manager score close to 1 whatever the other four
# do. The median top-holder share falls as the floor rises, which is the real
# mechanism behind the sweep: raising the holder floor works because it
# incidentally selects less concentrated names.
#
# The pair below is the highest-scoring one at a floor of half the managers,
# printed with each stock's largest single weight so the reader can see this
# happening rather than take it on trust.

# %%
if len(latest_holdings) > 0:
    min_holders = max(2, latest_holdings["cik"].n_unique() // 2)
    eligible = holder_counts >= min_holders
    pair_ok = eligible[row_idx] & eligible[col_idx]
    if pair_ok.any():
        candidates = np.flatnonzero(pair_ok)
        best = candidates[np.argmax(pair_values[candidates])]
        stock_a, stock_b = stock_list[row_idx[best]], stock_list[col_idx[best]]
        name_a = latest_holdings.filter(pl.col("cusip") == stock_a)["issuer"].first()
        name_b = latest_holdings.filter(pl.col("cusip") == stock_b)["issuer"].first()
        column_a = ownership_norm[:, row_idx[best]]
        column_b = ownership_norm[:, col_idx[best]]
        print(f"Highest co-ownership among stocks held by at least {min_holders} managers:")
        print(
            f"  {name_a} ({stock_a}), {holder_counts[row_idx[best]]} holders, "
            f"largest weight {column_a.max() / column_a.sum():.0%}"
        )
        print(
            f"  {name_b} ({stock_b}), {holder_counts[col_idx[best]]} holders, "
            f"largest weight {column_b.max() / column_b.sum():.0%}"
        )
        print(f"  Similarity: {pair_values[best]:.5f}")
    else:
        print(f"No pair of stocks is held by {min_holders} or more managers.")

# %% [markdown]
# The similarity still measures agreement in disclosed portfolio weights and
# still says nothing about return comovement.
#
# The check worth carrying out of this section is not the holder floor. It is
# to report a concentration alongside any similarity computed over a short
# vector, because the two together say whether the number rests on one
# observation or on several, and the similarity alone cannot.

# %% [markdown]
# ## Part 4: Institutional Ownership Change
#
# **Construction**: Aggregate change in institutional ownership across quarters.
# This notebook measures the construction; whether the resulting feature carries
# forward-return predictive content is an empirical question that downstream
# Chapter 11/12 pipelines evaluate against price data, not a claim made here.

# %% [markdown]
# ### Select comparable quarter snapshots
#
# Rename period-specific fields before joining the latest two reporting periods.


# %%
def select_stock_quarter(df: pl.DataFrame, period, suffix: str) -> pl.DataFrame:
    return df.filter(pl.col("report_period") == period).select(
        "cusip",
        pl.col("issuer_name").alias(f"issuer_{suffix}"),
        pl.col("quarter_value_usd").alias(f"value_{suffix}_usd"),
        pl.col("n_institutions").alias(f"n_institutions_{suffix}"),
    )


# %%
if len(complete_positions_df) > 0 and complete_positions_df["report_period"].n_unique() > 1:
    stock_quarter = complete_positions_df.group_by(["cusip", "report_period"]).agg(
        pl.col("issuer").first().alias("issuer_name"),
        pl.col("reported_value_usd").sum().alias("quarter_value_usd"),
        pl.col("cik").n_unique().alias("n_institutions"),
        pl.col("timestamp").max().alias("timestamp"),
    )
    comparison_periods = stock_quarter["report_period"].unique().sort(descending=True).head(2)
    current_period, prior_period = comparison_periods.to_list()
    current_availability = complete_positions_df.filter(pl.col("report_period") == current_period)[
        "timestamp"
    ].max()
    prior = select_stock_quarter(stock_quarter, prior_period, "q1")
    current = select_stock_quarter(stock_quarter, current_period, "q2")
    qoq = (
        prior.join(current, on="cusip", how="full", coalesce=True)
        .with_columns(
            pl.coalesce("issuer_q2", "issuer_q1").alias("issuer_name"),
            pl.lit(current_availability).alias("timestamp"),
            pl.col("value_q1_usd").fill_null(0),
            pl.col("value_q2_usd").fill_null(0),
            pl.col("n_institutions_q1").fill_null(0),
            pl.col("n_institutions_q2").fill_null(0),
        )
        .with_columns(
            (pl.col("value_q2_usd") - pl.col("value_q1_usd")).alias("value_change_usd"),
            pl.max_horizontal("n_institutions_q1", "n_institutions_q2").alias("n_institutions"),
            pl.when(pl.col("value_q1_usd") > 0)
            .then((pl.col("value_q2_usd") - pl.col("value_q1_usd")) / pl.col("value_q1_usd"))
            .otherwise(None)
            .alias("pct_change"),
        )
    )
else:
    qoq = None
    print("Need multiple quarters for ownership-change analysis")

# %% [markdown]
# ### Inspect ownership-change leaders and exits
#
# Use the quarter-over-quarter change table to identify broad institutional
# buying, selling, new entries, and full exits.
#
# The comparison runs between the two most recent quarters that every included
# manager filed for, so a manager missing from the newest quarter cannot read
# as a mass exit.

# %%
if qoq is not None:
    print("=== Institutional Ownership Changes ===")

    top_buys = (
        qoq.filter(pl.col("value_change_usd") > 0)
        .sort("value_change_usd", descending=True)
        .head(10)
    )
    print("\nTop 10 Institutional Buys (by $ change):")
    print(
        top_buys.select(
            [
                "issuer_name",
                pl.col("cusip").str.slice(-4).alias("cusip_tail"),
                "n_institutions",
                "value_q1_usd",
                "value_q2_usd",
                "value_change_usd",
            ]
        ).head(10)
    )

    top_sells = qoq.filter(pl.col("value_change_usd") < 0).sort("value_change_usd").head(10)
    print("\nTop 10 Institutional Sells (by $ change):")
    print(
        top_sells.select(
            [
                "issuer_name",
                pl.col("cusip").str.slice(-4).alias("cusip_tail"),
                "n_institutions",
                "value_q1_usd",
                "value_q2_usd",
                "value_change_usd",
            ]
        ).head(10)
    )

    new_positions = qoq.filter(pl.col("value_q1_usd") == 0).filter(pl.col("value_q2_usd") > 0)
    exits = qoq.filter(pl.col("value_q2_usd") == 0).filter(pl.col("value_q1_usd") > 0)
    print(f"\nNew positions initiated: {len(new_positions)}")
    print(f"Complete exits: {len(exits)}")

# %% [markdown]
# A new position and a full exit are both defined against zero disclosed
# value, so a manager crossing the disclosure threshold in either direction
# appears as one.

# %% [markdown]
# ## Part 5: Crowding descriptors
#
# Two quantities per stock. **Breadth** is the number of included managers
# holding it. **Ownership HHI** is the Herfindahl index of those managers'
# shares of the disclosed value, so it falls towards one over the holder count
# when they hold similar amounts and rises towards one when a single manager
# dominates.
#
# The crowding score below divides the first by the second, and the two decide
# the ranking together rather than one of them leading. Holder count sets the
# ceiling: `n` managers holding equal amounts give an HHI of one over `n` and a
# score of `n` squared, the most that many holders can score. Concentration
# then pulls a name down from its ceiling, and far enough that fewer holders
# can outrank more - three equal holders score nine, while four holders where
# one carries almost everything score about four.
#
# So it is a descriptive ordering within this manager universe, its magnitude
# carries no units and no meaning outside it, and reading it needs the two
# columns beside it. This notebook observes no trades, no liquidation and no
# price impact.

# %%
if len(latest_holdings) > 0:
    crowding = latest_holdings.group_by("cusip").agg(
        [
            pl.col("issuer").first().alias("issuer_name"),
            pl.col("cik").n_unique().alias("n_institutions"),
            pl.col("reported_value_usd").sum().alias("total_inst_value_usd"),
            # HHI of ownership (lower = more dispersed = higher crowding)
            (pl.col("reported_value_usd") / pl.col("reported_value_usd").sum())
            .pow(2)
            .sum()
            .alias("ownership_hhi"),
        ]
    )

# %%
if len(latest_holdings) > 0:
    crowding = crowding.with_columns(
        # Crowding score: more institutions + lower concentration = higher crowding
        (pl.col("n_institutions") / pl.col("ownership_hhi").clip(lower_bound=0.01)).alias(
            "crowding_score"
        )
    )
    if not crowding.select(
        pl.all_horizontal(
            pl.col("ownership_hhi").is_finite(), pl.col("crowding_score").is_finite()
        ).all()
    ).item():
        raise RuntimeError(
            "Crowding descriptors must be finite for every retained equity position."
        )
    crowding = crowding.sort(
        ["crowding_score", "total_inst_value_usd", "cusip"],
        descending=[True, True, False],
    )

    print("=== Crowding Descriptors ===")
    print("\nMost crowded positions (held by many funds with similar weights):")
    print(
        crowding.select(
            [
                "issuer_name",
                # Two share classes of one company are two CUSIPs and two rows.
                # Without the identifier they read as a duplicated row.
                pl.col("cusip").str.slice(-4).alias("cusip_tail"),
                "n_institutions",
                "total_inst_value_usd",
                "ownership_hhi",
                "crowding_score",
            ]
        ).head(15)
    )

    # Concentrated bets (few funds, high conviction)
    concentrated = crowding.filter(pl.col("n_institutions") == 1).sort(
        "total_inst_value_usd", descending=True
    )
    print(f"\nConcentrated bets (single-fund positions): {len(concentrated)}")
    if len(concentrated) > 0:
        display(
            concentrated.select(
                "issuer_name",
                pl.col("cusip").str.slice(-4).alias("cusip_tail"),
                "total_inst_value_usd",
            ).head(10)
        )

# %% [markdown]
# The high scores are the names most of these managers hold in comparable
# size. Whether that structure predicts liquidation pressure is an empirical
# question about prices, and nothing here touches prices.

# %% [markdown]
# ## Part 6: Institution Similarity Network
#
# Which institutions have similar portfolios? Useful for:
# - Identifying strategy clusters
# - Comparing common disclosed holdings
# - Understanding market structure


# %%
def build_portfolio_vectors(
    holdings: pl.DataFrame,
) -> tuple[list[str], dict[str, str], dict[str, np.ndarray]]:
    """Build normalized portfolio vectors keyed by institution CIK."""
    stocks = sorted(holdings["cusip"].unique().to_list())
    institutions = sorted(holdings["cik"].unique().to_list())
    inst_names = {
        row["cik"]: row["company_name"]
        for row in holdings.select(["cik", "company_name"])
        .sort(["cik", "company_name"])
        .unique(subset="cik", keep="first", maintain_order=True)
        .iter_rows(named=True)
    }

    stock_idx = {s: i for i, s in enumerate(stocks)}

    # Build portfolio vectors
    portfolios = {}
    for inst in institutions:
        inst_holdings = holdings.filter(pl.col("cik") == inst)
        vec = np.zeros(len(stocks))
        total_val = inst_holdings["reported_value_usd"].sum()
        if total_val > 0:
            for row in inst_holdings.iter_rows(named=True):
                vec[stock_idx[row["cusip"]]] = row["reported_value_usd"] / total_val
        portfolios[inst] = vec

    return institutions, inst_names, portfolios


# %% [markdown]
# ### Pairwise Institution Similarity
#
# Reuse the normalized portfolio vectors to compute cosine similarity between
# institutions. This highlights strategy overlap rather than stock-level
# co-ownership.
#
# %%
def compute_institution_similarity(holdings: pl.DataFrame) -> pl.DataFrame:
    """Compute pairwise similarity between institutions based on portfolio overlap."""
    institutions, inst_names, portfolios = build_portfolio_vectors(holdings)

    # Compute pairwise cosine similarity
    similarities = []
    for i, inst1 in enumerate(institutions):
        for inst2 in institutions[i + 1 :]:
            v1, v2 = portfolios[inst1], portfolios[inst2]
            norm1, norm2 = np.linalg.norm(v1), np.linalg.norm(v2)
            if norm1 > 0 and norm2 > 0:
                sim = np.dot(v1, v2) / (norm1 * norm2)
            else:
                sim = 0

            similarities.append(
                {
                    "inst1": inst_names.get(inst1, inst1),
                    "inst2": inst_names.get(inst2, inst2),
                    "similarity": sim,
                }
            )

    return pl.DataFrame(similarities).sort(
        ["similarity", "inst1", "inst2"],
        descending=[True, False, False],
    )


# %%
if len(latest_holdings) > 0 and latest_holdings["cik"].n_unique() > 1:
    inst_similarity = compute_institution_similarity(latest_holdings)

    print("=== Institution Similarity (Portfolio Overlap) ===")
    print("\nMost similar pairs:")
    display(inst_similarity.head(10))

    print("\nLeast similar pairs (most diversifying):")
    display(inst_similarity.tail(5))

# %% [markdown]
# This similarity is over portfolio weight vectors of several thousand
# dimensions each, so it does not saturate the way the stock-level one does.
# The quantity it measures is agreement in disclosed long equity weights, which
# is a fraction of what most of these managers run.

# %% [markdown]
# ## Part 7: Visualization
#
# These plots turn the ownership graph into portfolio diagnostics, separating
# breadth, conviction, crowding, and ownership change in a form a researcher can inspect.

# %%
if len(latest_holdings) > 0:
    # Plot 1: Holdings distribution by institution
    inst_stats = (
        latest_holdings.group_by(["cik", "company_name"])
        .agg(
            [
                pl.col("cusip").n_unique().alias("n_holdings"),
                (pl.col("reported_value_usd").sum() / 1e9).alias("total_value_usd_bn"),
            ]
        )
        .with_columns(pl.col("company_name").alias("institution_name"))
        .sort("total_value_usd_bn")
    )

    fig1 = go.Figure(
        go.Bar(
            x=inst_stats["total_value_usd_bn"],
            y=inst_stats["institution_name"],
            orientation="h",
            marker_color=COLORS["blue"],
            customdata=inst_stats["n_holdings"],
            hovertemplate="%{y}<br>Value: $%{x:.1f}B<br>Positions: %{customdata}<extra></extra>",
        )
    )
    fig1.update_layout(
        title="Disclosed position value by manager, latest complete quarter",
        xaxis_title="Reported position value (USD billions)",
        yaxis_title=None,
        height=500,
        showlegend=False,
        margin=dict(l=200),
    )
    show_plotly_with_alt(
        fig1,
        "A horizontal bar chart of ten managers' disclosed long-equity value in billions of "
        "dollars, longest at the top. Berkshire Hathaway leads by a wide margin, AQR Capital "
        "follows, then Citadel, Millennium and D. E. Shaw close together at about half "
        "Berkshire's length. Renaissance, Point72, Tiger Global and Bridgewater are shorter "
        "again, and Two Sigma Securities is last with a bar barely distinguishable from zero.",
    )

# %% [markdown]
# Length is disclosed dollars; the position count is on hover. A manager short
# and wide holds many small positions, one long and narrow holds few large
# ones, and neither is visible from the bar alone.

# %%
if len(latest_holdings) > 0:
    # Plot 2: Top holdings across all institutions
    top_stocks = (
        latest_holdings.group_by("cusip")
        .agg(
            [
                pl.col("issuer").first().alias("issuer"),
                pl.col("cik").n_unique().alias("n_institutions"),
                (pl.col("reported_value_usd").sum() / 1e9).alias("total_value_usd_bn"),
            ]
        )
        .sort(
            ["n_institutions", "total_value_usd_bn", "cusip"],
            descending=[True, True, False],
        )
        .head(20)
        .with_columns(
            (pl.col("issuer") + pl.lit(" [") + pl.col("cusip").str.slice(-4) + pl.lit("]")).alias(
                "display_label"
            )
        )
    )

# %% [markdown]
# Use a horizontal bar chart for the deterministic breadth-first selection.
# The CUSIP suffix makes every categorical label unique.

# %%
if len(latest_holdings) > 0:
    top_stocks_pd = top_stocks.sort("total_value_usd_bn", descending=False).to_pandas()
    fig2 = go.Figure(
        go.Bar(
            x=top_stocks_pd["total_value_usd_bn"],
            y=top_stocks_pd["display_label"],
            orientation="h",
            marker_color=COLORS["blue"],
            customdata=top_stocks_pd["n_institutions"],
            hovertemplate="%{y}<br>Value: $%{x:.1f}B<br>Managers: %{customdata}<extra></extra>",
        )
    )
    fig2.update_layout(
        title="The twenty most broadly held disclosed positions",
        xaxis_title="Reported position value (USD billions)",
        yaxis_title=None,
        height=600,
        margin=dict(l=330),
    )
    show_plotly_with_alt(
        fig2,
        "A horizontal bar chart of twenty holdings, each labelled with the issuer name and the "
        "last four characters of its CUSIP, longest at the top. Apple is roughly twice the "
        "length of the second bar and the lengths fall away steeply after the first five, with "
        "the last several close to zero. Two rows carry the same issuer name with different "
        "CUSIP suffixes, which are its two share classes.",
    )

# %% [markdown]
# Selection here is by breadth first and value second, so the ordering by bar
# length is not the ordering that chose the twenty. Breadth is a description of
# who discloses a name, not evidence about what it will do.

# %% [markdown]
# Selection is by the SIZE of the move rather than by its sign. Sorting on the
# signed change and taking the head puts only increases on a chart whose zero
# lines invite reading four quadrants.

# %%
if qoq is not None and len(qoq) > 0:
    momentum_plot = (
        qoq.filter(pl.col("n_institutions") >= 2)
        .filter(pl.col("pct_change").is_not_null())
        .sort(pl.col("value_change_usd").abs(), descending=True)
    )

    if len(momentum_plot) > 0:
        mom_pd = momentum_plot.head(50).to_pandas()
        mom_pd["pct_change_pct"] = (100 * mom_pd["pct_change"]).clip(lower=-100, upper=500)
        mom_pd["value_change_usd_bn"] = mom_pd["value_change_usd"] / 1e9
        fig3 = go.Figure(
            go.Scatter(
                x=mom_pd["pct_change_pct"],
                y=mom_pd["value_change_usd_bn"],
                mode="markers",
                marker=dict(color=COLORS["blue"], size=9, opacity=0.75),
                text=mom_pd["issuer_name"],
                hovertemplate=(
                    "%{text}<br>Change: %{x:.1f}%<br>Value change: $%{y:.2f}B<extra></extra>"
                ),
            )
        )
        fig3.update_layout(
            title="Quarter-over-quarter ownership change, percentage against dollars",
            xaxis_title="Change in reported value (%, clipped to [-100, 500])",
            yaxis_title="Change in reported value (USD billions)",
            height=520,
            showlegend=False,
        )
        fig3.add_hline(y=0, line_dash="dash", line_color=COLORS["neutral"])
        fig3.add_vline(x=0, line_dash="dash", line_color=COLORS["neutral"])
        show_plotly_with_alt(
            fig3,
            "A scatter of fifty holdings, percentage change in reported value on the horizontal "
            "axis against dollar change in billions on the vertical, with dashed reference lines at "
            "zero on both. The points form a low band close to the horizontal zero line and spread "
            "the full width of the percentage axis; two sit far above the band at a modest "
            "percentage change, and two sit at the far right of the percentage axis with a small "
            "dollar change. The two axes rank the same holdings differently.",
        )

# %% [markdown]
# The fifty largest moves by absolute dollar change, in both directions. The
# horizontal axis is clipped at the bounds its own label names, so a point on
# either edge is at or beyond the cap rather than exactly at it.
#
# Both axes are here because they disagree. A large percentage change on a
# small base is a small dollar change, and the points furthest to the right are
# not the ones furthest up.

# %% [markdown]
# ## Part 8: Feature Engineering for ML Models
#
# Create point-in-time features that can be joined to price data for validation.

# %%
if len(latest_holdings) > 0:
    # Stock-level features for ML
    stock_features = (
        latest_holdings.group_by("cusip")
        .agg(
            [
                pl.col("issuer").first().alias("issuer_name"),
                # Ownership breadth
                pl.col("cik").n_unique().alias("n_inst_holders"),
                # Value concentration
                pl.col("reported_value_usd").sum().alias("total_inst_value_usd"),
                pl.col("reported_value_usd").mean().alias("avg_position_size_usd"),
                pl.col("reported_value_usd").std().fill_null(0).alias("position_size_std_usd"),
                pl.col("timestamp").max().alias("timestamp"),
                # Ownership concentration (HHI)
                (pl.col("reported_value_usd") / pl.col("reported_value_usd").sum())
                .pow(2)
                .sum()
                .alias("ownership_hhi"),
            ]
        )
        .with_columns(
            [
                # Breadth over the managers in the graph, the producer's denominator.
                (pl.col("n_inst_holders") / latest_holdings["cik"].n_unique()).alias(
                    "inst_coverage_pct"
                ),
                (
                    pl.col("position_size_std_usd")
                    / pl.col("avg_position_size_usd").clip(lower_bound=1)
                ).alias("position_cv"),
            ]
        )
        .sort("cusip")
    )

    print("=== Stock-Level Features for ML ===")
    print(f"Features generated for {len(stock_features)} stocks")
    print("\nFeature summary:")
    print(stock_features.describe())

# %% [markdown]
# Every feature is as of a quarter end and becomes usable at the availability
# timestamp, not at the quarter end. How long any of them stays informative is
# not established here.
# %%
if len(latest_holdings) > 0:
    # Add momentum features if available
    if qoq is not None and len(qoq) > 0:
        momentum_features = qoq.select(
            [
                "cusip",
                pl.col("value_change_usd").alias("inst_value_change_usd"),
                pl.col("pct_change").alias("inst_pct_change"),
            ]
        )
        stock_features = (
            stock_features.join(momentum_features, on="cusip", how="left")
            .with_columns(pl.col("inst_value_change_usd").fill_null(0))
            .sort("cusip")
        )
        print("Added momentum features")
    else:
        # One complete quarter: the producer still emits both columns, so match it.
        stock_features = stock_features.with_columns(
            pl.lit(0.0, dtype=pl.Float64).alias("inst_value_change_usd"),
            pl.lit(None, dtype=pl.Float64).alias("inst_pct_change"),
        ).sort("cusip")
        print("Single complete quarter: momentum columns emitted as 0.0 / null")

    display(stock_features.head(10))

# %% [markdown]
# ### Canonical artifact parity
#
# Confirm that the downloader's latest-quarter edge and feature artifacts are
# the same objects constructed above, rather than stale snapshots.

# %%
if len(latest_holdings) > 0:
    expected_edges = latest_holdings.select(
        pl.col("cik").alias("institution_id"),
        pl.col("cusip").alias("stock_id"),
        pl.col("company_name").alias("institution_name"),
        pl.col("issuer").alias("stock_name"),
        pl.col("reported_value_usd").alias("weight_value"),
        pl.col("shares").alias("weight_shares"),
        pl.col("report_period").alias("report_date"),
        "timestamp",
    )
    canonical_edges = load_13f_edges()
    canonical_features = load_13f_stock_features()
    assert_frame_equal(
        expected_edges.sort(["institution_id", "stock_id"]),
        canonical_edges.sort(["institution_id", "stock_id"]),
        check_row_order=True,
    )
    assert_frame_equal(
        stock_features.sort("cusip"),
        canonical_features.sort("cusip"),
        check_row_order=True,
        rel_tol=1e-6,
    )
    print("Canonical edge and stock-feature artifact parity: PASS")

# %% [markdown]
# The assertion above is the point of the section: this notebook reconstructs
# what the downloader wrote and checks the two frames are equal, so a reader
# can see how the shipped artifact was built rather than taking it on trust. A
# drift between them fails here instead of surfacing as a puzzling number in
# Chapter 23.

# %% [markdown]
# ## Part 9: Artifacts on Disk
#
# The canonical downloader writes all graph artifacts (holdings, edge list,
# stock features, co-ownership matrix, stock list) to
# `$ML4T_DATA_PATH/equities/positioning/13f/`. Chapter 23 notebooks read
# those files directly via `load_13f_edges()` and `load_13f_stock_features()`.
# This notebook is a consumer of the holdings artifact, not a producer - its
# derived tables (above) are for inspection and pedagogy only.

# %%
print("=== Canonical 13F Artifacts ===")
print("Writer:    data/equities/positioning/13f_download.py")
print("Location:  $ML4T_DATA_PATH/equities/positioning/13f/")
print("Files:     institutional_holdings.parquet")
print("           institution_stock_edges.parquet")
print("           stock_features.parquet")
print("           coownership_matrix.npy")
print("           coownership_stocks.txt")
print("Loaders:   load_institutional_holdings_13f(), load_13f_edges(),")
print("           load_13f_stock_features()")

# %% [markdown]
# ## Results interpretation
#
# **Co-ownership structure.** This graph is not sparse, and the numbers to read
# it by are printed in Part 2 and Part 3 rather than asserted here: the
# bipartite density, the share of stock pairs sharing no holder, and the share
# sitting at the top of the similarity scale. Ten large managers holding a few
# thousand names each produce a densely connected graph, and the similarity
# saturates because each stock is described by ten numbers. Both facts are
# properties of the manager universe rather than of institutional ownership,
# and widening the universe changes them.
#
# **Institutional ownership change.** Quarter-over-quarter changes describe how
# aggregate reported holdings moved between the two most recent quarters every
# included manager filed for. The availability timestamp records when that
# snapshot became observable. No persistence or forward-return claim is made or
# tested.
#
# **Crowding.** The score is breadth divided by ownership concentration, and
# Part 5 says what that makes it: holder count sets a ceiling of its square,
# and concentration pulls a name below that ceiling by enough that fewer,
# evenly weighted holders can outrank more uneven ones. It describes disclosed
# structure. It does not observe liquidation or price impact, and it is not on
# a scale that means anything outside this manager universe.

# %% [markdown]
# ## Summary: What We Can Do With 13F Data
#
# ### Implemented Features
#
# | Feature | Description | Use Case |
# |---------|-------------|----------|
# | `n_inst_holders` | Number of institutions holding stock | Crowding risk |
# | `total_inst_value_usd` | Total reported position value (USD) | Ownership scale |
# | `ownership_hhi` | Concentration of ownership | Crowding risk |
# | `inst_value_change_usd` | Quarter-over-quarter value change | Ownership change |
# | `inst_pct_change` | Fractional change in reported value | Ownership change |
# | Co-ownership matrix | Stock-stock similarity | Clustering, GNN |

# %%
print("\n=== Analysis Summary ===")
if len(positions_df) > 0:
    print(f"Institutions: {positions_df['cik'].n_unique()}")
    print(f"Unique stocks: {positions_df['cusip'].n_unique()}")
    print(f"Aggregated positions: {len(positions_df):,}")
    try:
        print(f"Stock features (derived): {len(stock_features)}")
    except NameError:
        print("Stock features (derived): 0")

# %% [markdown]
# ## Key takeaways
#
# 1. SEC 13F filings provide a structured, machine-readable view of institutional
#    equity ownership. The canonical downloader at
#    `data/equities/positioning/13f_download.py` walks EDGAR and writes a
#    normalized holdings artifact consumed here via `load_institutional_holdings_13f()`.
# 2. **A cosine's effective dimension is set by its weights, not by its
#    non-zeros.** Each stock here is described by ten numbers, one per manager,
#    and over a third are held by exactly one - two such stocks score exactly 1
#    whenever that manager is the same, which is why millions of pairs sit at
#    the top of the scale and "the highest-similarity pair" is an arbitrary pick
#    from a tie. Requiring more holders thins that out, but the top pair is
#    still at 1 with five holders each, because one manager carries the great
#    majority of both positions. Part 3 measures both, and the check to carry
#    away is to report a concentration next to any similarity computed over a
#    short vector.
# 3. **The crowding score mixes two things and neither dominates.** Holder
#    count over ownership HHI reaches its maximum, the square of the holder
#    count, only when those holders are equally weighted; concentration pulls a
#    name below that, far enough that three equal holders can outrank four with
#    one dominant. It is not a breadth ranking with a tie-break, and its
#    magnitude means nothing outside this manager universe. Quarter-over-quarter
#    change and concentration are descriptive candidates whose predictive value
#    requires a point-in-time return study.
# 4. **The identity is the CIK and the name comes from the filing.** A
#    hand-written display name that disagrees with the filer renames a manager
#    in every table downstream, and this notebook carried one: the CIK labelled
#    "Two Sigma Investments" files as Two Sigma Securities, a different book.
# 5. The 45-day filing deadline limits real-time use; `timestamp` records when
#    the complete included-manager snapshot becomes available.
#
# **Chapter Connections**:
# - **Chapter 23 (Knowledge Graphs)**: Use the bipartite graph for GNN message passing
# - **Chapter 11 (ML Pipeline)**: Join features to price data for cross-sectional models
# - **Chapter 12 (Gradient Boosting)**: Use crowding and ownership change as tree model features
# - **Chapter 24 (Autonomous Agents)**: Natural language queries about institutional holdings
#
# **Limitations**:
# - Only long equity positions (no shorts, no derivatives)
# - >$100M AUM threshold misses smaller funds
# - Confidential treatment exemptions hide some positions
#
# **Next**: Chapter 23 converts these ownership links into structured graph
# representations, while Chapter 24 uses the same entities in agentic workflows.

```