fix is_in for empty lists (#2679)

pola-rs · Feb 17, 2022 · 4faa427 · 4faa427
1 parent 83d5499
commit 4faa427
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diff --git a/polars/polars-lazy/src/dsl/mod.rs b/polars/polars-lazy/src/dsl/mod.rs
@@ -1394,6 +1394,15 @@ impl Expr {
     #[cfg_attr(docsrs, doc(cfg(feature = "is_in")))]
     pub fn is_in(self, other: Expr) -> Self {
         let has_literal = has_root_literal_expr(&other);
+        if has_literal {
+            if let Expr::Literal(LiteralValue::Series(s)) = &other {
+                // nothing is in an empty list return all False
+                if s.is_empty() {
+                    return Expr::Literal(LiteralValue::Boolean(false));
+                }
+            }
+        }
+
         let f = |s: &mut [Series]| {
             let left = &s[0];
             let other = &s[1];

diff --git a/py-polars/tests/test_df.py b/py-polars/tests/test_df.py
@@ -1892,3 +1892,9 @@ def test_categorical_outer_join() -> None:
     expected = pl.DataFrame({"val1": [1], "key1": [42], "key2": ["bar"], "val2": [2]})
 
     assert out.frame_equal(expected)
+
+
+def test_empty_is_in() -> None:
+    assert pl.DataFrame({"foo": ["a", "b", "c", "d"]}).filter(
+        pl.col("foo").is_in([])
+    ).shape == (0, 1)