From e2790d2d5dea8dc980958728efa1ec6f2b5b1e90 Mon Sep 17 00:00:00 2001
From: Guilherme Schardong <guilherme.schardong@isr.uc.pt>
Date: Wed, 6 May 2026 16:26:52 +0100
Subject: [PATCH] Moving the `gini` function to `metrics.py`.

---
 src/facebias/metrics.py | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/src/facebias/metrics.py b/src/facebias/metrics.py
index fa4c8cd..427a4cb 100644
--- a/src/facebias/metrics.py
+++ b/src/facebias/metrics.py
@@ -1,6 +1,9 @@
 # -*- coding: utf-8 -*-
 
+"""Model evaluation metrics."""
+
 import logging
+from itertools import combinations
 from pathlib import Path
 from typing import Any
 
@@ -86,7 +89,7 @@ def binary_fpr_fnr(cm: np.ndarray) -> dict[str, np.number]:
 
 def multiclass_fpr_fnr(
     gt: pd.Series, preds: pd.Series, labels: list[Any] | None = None
-):
+) -> tuple[dict, list[str]]:
     """Calculates one-vs-rest false-positive and negative rates for each class.
 
     Also returns the counts of false-positives, false-negatives, true-positives
@@ -128,7 +131,7 @@ def multiclass_fpr_fnr(
     return results, labels
 
 
-def _agreement_sanity_checks(x_pred: pd.Series, y_pred: pd.Series):
+def _agreement_sanity_checks(x_pred: pd.Series, y_pred: pd.Series) -> bool:
     if len(x_pred) != len(y_pred):
         raise ValueError(
             f"Predictions have different lengths. len(x_pred) = {len(x_pred)}"
@@ -140,7 +143,7 @@ def _agreement_sanity_checks(x_pred: pd.Series, y_pred: pd.Series):
     return True
 
 
-def agreement_fraction(x_pred: pd.Series, y_pred: pd.Series):
+def agreement_fraction(x_pred: pd.Series, y_pred: pd.Series) -> float:
     """Calculates the fraction of agreement between predictions by two models.
 
     Note that the predictions must both have the same indices and lengths.
@@ -169,7 +172,7 @@ def agreement_fraction(x_pred: pd.Series, y_pred: pd.Series):
 
 def agreement_elements(
     x_pred: pd.Series, y_pred: pd.Series, return_disagreement: bool = True
-):
+) -> tuple[pd.Series, pd.Series | None]:
     """Returns the elements of agreement, and optionally, disagreement between models.
 
     Note that, as in `agreement_fraction`, the predictions must have the same
@@ -209,6 +212,13 @@ def agreement_elements(
         return idx[x_pred == y_pred], None
 
 
+def gini(x: list[float]) -> float:
+    x = np.array(x, dtype=np.float32)
+    n = len(x)
+    diffs = sum(abs(i - j) for i, j in combinations(x, r=2))
+    return (diffs / (n**2 * x.mean())).item()
+
+
 # TODO(gschardong): Move to the same file as `load_dataset`
 def _to_age_bracket(row):
     iage = int(row["age"])