fix: Prevent join panic when suffix="" and coalesce=True

crates/polars-ops/src/frame/join/general.rs

@@ -56,30 +56,44 @@ pub fn _coalesce_full_join(
     suffix: Option<PlSmallStr>,
     df_left: &DataFrame,
 ) -> DataFrame {
-    // No need to allocate the schema because we already
-    // know for certain that the column name for left is `name`
-    // and for right is `name + suffix`
     let schema_left = if keys_left == keys_right {
         Arc::new(Schema::default())
     } else {
         df_left.schema().clone()
     };
 
-    let schema = df.schema().clone();
     let mut to_remove = Vec::with_capacity(keys_right.len());
-
-    let columns = unsafe { df.columns_mut() };
     let suffix = get_suffix(suffix);
+
+    let mut index_pairs: Vec<(usize, usize)> = Vec::with_capacity(keys_left.len());
     for (l, r) in keys_left.iter().zip(keys_right.iter()) {
-        let pos_l = schema.get_full(l.as_str()).unwrap().0;
+        let pos_l = df
+            .columns()
+            .iter()
+            .enumerate()
+            .find(|(_, col)| col.name() == l.as_str())
+            .unwrap()
+            .0;
 
         let r = if l == r || schema_left.contains(r.as_str()) {
             _join_suffix_name(r.as_str(), suffix.as_str())
         } else {
             r.clone()
         };
-        let pos_r = schema.get_full(&r).unwrap().0;
+        let pos_r = df
+            .columns()
+            .iter()
+            .enumerate()
+            .skip(pos_l + 1)
+            .find(|(_, col)| col.name() == r.as_str())
+            .unwrap()
+            .0;
+
+        index_pairs.push((pos_l, pos_r));
+    }
 
+    let columns = unsafe { df.columns_mut() };
+    for (pos_l, pos_r) in index_pairs {
         let l = columns[pos_l].clone();
         let r = columns[pos_r].clone();
 

py-polars/tests/unit/operations/test_join.py

@@ -4025,3 +4025,20 @@ def test_full_join_rewrite_to_right_with_cast() -> None:
         },
     )
     assert_frame_equal(out, ret, check_column_order=True, check_row_order=False)
+
+
+def test_full_join_coalesce_empty_suffix_27368() -> None:
+    df1 = pl.DataFrame({"a": [0, 1], "b": [10, 11]})
+    df2 = pl.DataFrame({"a": [1, 2], "c": [11, 12]})
+
+    result = df1.join(df2, how="full", on="a", coalesce=True, suffix="")
+
+    expected = pl.DataFrame(
+        {
+            "a": [0, 1, 2],
+            "b": [10, 11, None],
+            "c": [None, 11, 12],
+        }
+    )
+
+    assert_frame_equal(result, expected, check_row_order=False)