From d336eb63b1524f1c1da52ee110c07cde80c166ed Mon Sep 17 00:00:00 2001
From: Marco Gorelli <33491632+MarcoGorelli@users.noreply.github.com>
Date: Thu, 23 May 2024 15:37:18 +0200
Subject: [PATCH] feat!: remove redundant column name when pivoting by multiple
 values

---
 crates/polars-ops/src/frame/pivot/mod.rs      |  3 +-
 py-polars/polars/dataframe/frame.py           | 16 ++++-----
 py-polars/tests/unit/operations/test_pivot.py | 36 +++++++++----------
 3 files changed, 27 insertions(+), 28 deletions(-)

diff --git a/crates/polars-ops/src/frame/pivot/mod.rs b/crates/polars-ops/src/frame/pivot/mod.rs
index cec9ddd01cdb..6b045dc418bc 100644
--- a/crates/polars-ops/src/frame/pivot/mod.rs
+++ b/crates/polars-ops/src/frame/pivot/mod.rs
@@ -304,8 +304,7 @@ fn pivot_impl_single_column(
             let headers = column_agg.unique_stable()?.cast(&DataType::String)?;
             let mut headers = headers.str().unwrap().clone();
             if values.len() > 1 {
-                // TODO! MILESTONE 1.0: change to `format!("{value_col_name}{sep}{v}")`
-                headers = headers.apply_values(|v| Cow::from(format!("{value_col_name}{sep}{column}{sep}{v}")))
+                headers = headers.apply_values(|v| Cow::from(format!("{value_col_name}{sep}{v}")))
             }
 
             let n_cols = headers.len();
diff --git a/py-polars/polars/dataframe/frame.py b/py-polars/polars/dataframe/frame.py
index 086c9945a36b..e24b4e53d90c 100644
--- a/py-polars/polars/dataframe/frame.py
+++ b/py-polars/polars/dataframe/frame.py
@@ -7730,14 +7730,14 @@ def pivot(
         ...     separator="/",
         ... )
         shape: (2, 5)
-        ┌─────┬───────────┬───────────┬───────────┬───────────┐
-        │ ix  ┆ foo/col/a ┆ foo/col/b ┆ bar/col/a ┆ bar/col/b │
-        │ --- ┆ ---       ┆ ---       ┆ ---       ┆ ---       │
-        │ i64 ┆ i64       ┆ i64       ┆ i64       ┆ i64       │
-        ╞═════╪═══════════╪═══════════╪═══════════╪═══════════╡
-        │ 1   ┆ 1         ┆ 7         ┆ 2         ┆ 9         │
-        │ 2   ┆ 4         ┆ 1         ┆ 0         ┆ 4         │
-        └─────┴───────────┴───────────┴───────────┴───────────┘
+        ┌─────┬───────┬───────┬───────┬───────┐
+        │ ix  ┆ foo/a ┆ foo/b ┆ bar/a ┆ bar/b │
+        │ --- ┆ ---   ┆ ---   ┆ ---   ┆ ---   │
+        │ i64 ┆ i64   ┆ i64   ┆ i64   ┆ i64   │
+        ╞═════╪═══════╪═══════╪═══════╪═══════╡
+        │ 1   ┆ 1     ┆ 7     ┆ 2     ┆ 9     │
+        │ 2   ┆ 4     ┆ 1     ┆ 0     ┆ 4     │
+        └─────┴───────┴───────┴───────┴───────┘
         """  # noqa: W505
         index = _expand_selectors(self, index)
         columns = _expand_selectors(self, columns)
diff --git a/py-polars/tests/unit/operations/test_pivot.py b/py-polars/tests/unit/operations/test_pivot.py
index 7b63963cc559..0607583f82d4 100644
--- a/py-polars/tests/unit/operations/test_pivot.py
+++ b/py-polars/tests/unit/operations/test_pivot.py
@@ -48,16 +48,16 @@ def test_pivot_no_values() -> None:
     expected = pl.DataFrame(
         {
             "foo": ["A", "B", "C"],
-            "N1_bar_k": [1, None, None],
-            "N1_bar_l": [2, None, None],
-            "N1_bar_m": [None, 2, None],
-            "N1_bar_n": [None, 4, None],
-            "N1_bar_o": [None, None, 2],
-            "N2_bar_k": [1, None, None],
-            "N2_bar_l": [2, None, None],
-            "N2_bar_m": [None, 2, None],
-            "N2_bar_n": [None, 4, None],
-            "N2_bar_o": [None, None, 2],
+            "N1_k": [1, None, None],
+            "N1_l": [2, None, None],
+            "N1_m": [None, 2, None],
+            "N1_n": [None, 4, None],
+            "N1_o": [None, None, 2],
+            "N2_k": [1, None, None],
+            "N2_l": [2, None, None],
+            "N2_m": [None, 2, None],
+            "N2_n": [None, 4, None],
+            "N2_o": [None, None, 2],
         }
     )
 
@@ -195,10 +195,10 @@ def test_pivot_multiple_values_column_names_5116() -> None:
     )
     expected = {
         "c1": ["A", "B"],
-        "x1|c2|C": [1, 2],
-        "x1|c2|D": [3, 4],
-        "x2|c2|C": [8, 7],
-        "x2|c2|D": [6, 5],
+        "x1|C": [1, 2],
+        "x1|D": [3, 4],
+        "x2|C": [8, 7],
+        "x2|D": [6, 5],
     }
     assert result.to_dict(as_series=False) == expected
 
@@ -221,10 +221,10 @@ def test_pivot_duplicate_names_7731() -> None:
     ).to_dict(as_series=False)
     expected = {
         "b": [1.5, 2.5],
-        'a_{"c","e"}_{"x","x"}': [1, None],
-        'a_{"c","e"}_{"x","y"}': [None, 4],
-        'd_{"c","e"}_{"x","x"}': [7, None],
-        'd_{"c","e"}_{"x","y"}': [None, 8],
+        'a_{"x","x"}': [1, None],
+        'a_{"x","y"}': [None, 4],
+        'd_{"x","x"}': [7, None],
+        'd_{"x","y"}': [None, 8],
     }
     assert result == expected