fix stackoverflow in unique of empty series (#4389)

pola-rs · Aug 13, 2022 · fcbd488 · fcbd488
1 parent 614b9dd
commit fcbd488
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diff --git a/polars/polars-core/src/chunked_array/ops/unique/mod.rs b/polars/polars-core/src/chunked_array/ops/unique/mod.rs
@@ -177,6 +177,10 @@ where
     ChunkedArray<T>: IntoSeries,
 {
     fn unique(&self) -> Result<Self> {
+        // prevent stackoverflow repeated sorted.unique call
+        if self.is_empty() {
+            return Ok(self.clone());
+        }
         match self.is_sorted2() {
             IsSorted::Ascending | IsSorted::Descending => {
                 let mask = self.not_equal(&self.shift(1));

diff --git a/py-polars/tests/test_exprs.py b/py-polars/tests/test_exprs.py
@@ -313,3 +313,9 @@ def test_rank_so_4109() -> None:
             [1.0, 2.0, 3.0, 4.0],
         ],
     }
+
+
+def test_unique_empty() -> None:
+    for dt in [pl.Utf8, pl.Boolean, pl.Int32, pl.UInt32]:
+        s = pl.Series([], dtype=dt)
+        assert s.unique().series_equal(s)