From 515218df895e2788c9451af6764c1235817fe0f5 Mon Sep 17 00:00:00 2001
From: Auguste Baum <auguste@probabl.ai>
Date: Wed, 16 Oct 2024 17:59:11 +0200
Subject: [PATCH] add average score horizontal rule to cross-val chart

---
 skore/src/skore/item/cross_validation_item.py | 44 ++++++++++++-------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/skore/src/skore/item/cross_validation_item.py b/skore/src/skore/item/cross_validation_item.py
index 2976c570..68e0f700 100644
--- a/skore/src/skore/item/cross_validation_item.py
+++ b/skore/src/skore/item/cross_validation_item.py
@@ -54,23 +54,35 @@ def plot_cross_validation(cv_results: dict) -> altair.Chart:
         fields=["metric"], bind=input_dropdown, value="test_score"
     )
 
-    return (
-        altair.Chart(df, title="Cross-validation scores per split")
-        .mark_bar()
+    average_score_rule = (
+        altair.Chart(df)
+        .mark_rule(strokeWidth=2)
         .encode(
-            altair.X("split:N").axis(
-                title="Split number",
-                labelAngle=0,
-            ),
-            altair.Y("score:Q").axis(
-                title="Score",
-                titleAngle=0,
-                titleAlign="left",
-                titleX=0,
-                titleY=-5,
-                labelLimit=300,
-            ),
-            tooltip=["metric:N", "split:N", "score:Q"],
+            y="mean(score):Q",
+            tooltip=["mean(score):Q"],
+        )
+    )
+
+    return (
+        (
+            altair.Chart(df, title="Cross-validation scores per split")
+            .mark_bar()
+            .encode(
+                altair.X("split:N").axis(
+                    title="Split number",
+                    labelAngle=0,
+                ),
+                altair.Y("score:Q").axis(
+                    title="Score",
+                    titleAngle=0,
+                    titleAlign="left",
+                    titleX=0,
+                    titleY=-5,
+                    labelLimit=300,
+                ),
+                tooltip=["metric:N", "split:N", "score:Q"],
+            )
+            + average_score_rule
         )
         .add_params(selection)
         .transform_filter(selection)