scikit-learn · DeaMariaLeon · Nov 14, 2025 · Nov 14, 2025 · Nov 17, 2025 · Nov 24, 2025
diff --git a/doc/whats_new/upcoming_changes/sklearn.compose/32713.fix.rst b/doc/whats_new/upcoming_changes/sklearn.compose/32713.fix.rst
@@ -0,0 +1,4 @@
+- The dotted line for :class:`compose.ColumnTransformer` in its HTML display
+  now includes only its elements. The behaviour when a remainder is used,
+  has also been corrected.
+  By :user:`Dea María Léon <deamarialeon>`
diff --git a/sklearn/compose/_column_transformer.py b/sklearn/compose/_column_transformer.py
@@ -1237,7 +1237,7 @@ def _sk_visual_block_(self):
                 self.transformers, [("remainder", self.remainder, remainder_columns)]
             )
         else:
-            transformers = chain(self.transformers, [("remainder", self.remainder, "")])
+            transformers = chain(self.transformers, [("remainder", self.remainder, [])])
 
         names, transformers, name_details = zip(*transformers)
         return _VisualBlock(

diff --git a/sklearn/compose/tests/test_column_transformer.py b/sklearn/compose/tests/test_column_transformer.py
@@ -1538,7 +1538,7 @@ def test_sk_visual_block_remainder(remainder):
     )
     visual_block = ct._sk_visual_block_()
     assert visual_block.names == ("ohe", "remainder")
-    assert visual_block.name_details == (["col1", "col2"], "")
+    assert visual_block.name_details == (["col1", "col2"], [])
     assert visual_block.estimators == (ohe, remainder)
 
 

diff --git a/sklearn/utils/_repr_html/estimator.py b/sklearn/utils/_repr_html/estimator.py
@@ -184,10 +184,11 @@ def _write_label_html(
                 f'<a class="sk-estimator-doc-link {is_fitted_css_class}"'
                 f' rel="noreferrer" target="_blank" href="{doc_link}">?{doc_label}</a>'
             )
-
+        if name == "passthrough" or name_details == "[]":
+            name_caption = ""
         name_caption_div = (
             ""
-            if name_caption is None
+            if name_caption is None or name_caption == ""
             else f'<div class="caption">{html.escape(name_caption)}</div>'
         )
         name_caption_div = f"<div><div>{name}</div>{name_caption_div}</div>"
@@ -196,10 +197,13 @@ def _write_label_html(
             if doc_link or is_fitted_icon
             else ""
         )
+        label_arrow_class = (
+            "" if name == "passthrough" else "sk-toggleable__label-arrow"
+        )
 
         label_html = (
             f'<label for="{est_id}" class="sk-toggleable__label {is_fitted_css_class} '
-            f'sk-toggleable__label-arrow">{name_caption_div}{links_div}</label>'
+            f'{label_arrow_class}">{name_caption_div}{links_div}</label>'
         )
 
         fmt_str = (
@@ -212,6 +216,8 @@ def _write_label_html(
         if params:
             fmt_str = "".join([fmt_str, f"{params}</div>"])
         elif name_details and ("Pipeline" not in name):
+            if name == "passthrough" or name_details == "[]":
+                name_details = ""
             fmt_str = "".join([fmt_str, f"<pre>{name_details}</pre></div>"])
 
         out.write(fmt_str)
@@ -382,7 +388,10 @@ def _write_estimator_html(
 
         out.write("</div></div>")
     elif est_block.kind == "single":
-        if hasattr(estimator, "_get_params_html"):
+        if (
+            hasattr(estimator, "_get_params_html")
+            and not est_block.names == "passthrough"
+        ):
             params = estimator._get_params_html(doc_link=doc_link)._repr_html_inner()
         else:
             params = ""