fix div by zero (#3031)

pola-rs · Apr 1, 2022 · 524f8a5 · 524f8a5
1 parent b12a2e8
commit 524f8a5
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Showing 2 changed files with 19 additions and 1 deletion.
diff --git a/polars/polars-core/src/frame/groupby/mod.rs b/polars/polars-core/src/frame/groupby/mod.rs
@@ -144,7 +144,7 @@ impl DataFrame {
 
                     // arbitrarily chosen bound, if avg no of bytes to encode is larger than this
                     // value we fall back to default groupby
-                    if (lhs.get_values_size() + rhs.get_values_size()) / lhs.len() < 128 {
+                    if (lhs.get_values_size() + rhs.get_values_size()) / (lhs.len() + 1) < 128 {
                         pack_utf8_columns(lhs, rhs, n_partitions, sorted)
                     } else {
                         groupby_threaded_multiple_keys_flat(keys_df, n_partitions, sorted)

diff --git a/polars/tests/it/lazy/queries.rs b/polars/tests/it/lazy/queries.rs
@@ -90,3 +90,21 @@ fn test_special_groupby_schemas() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn max_on_empty_df_3027() -> Result<()> {
+    let df = df! {
+        "id" => ["1"],
+        "name" => ["one"],
+        "numb" => [1]
+    }?
+    .head(Some(0));
+
+    let out = df
+        .lazy()
+        .groupby(&[col("id"), col("name")])
+        .agg(&[col("numb").max()])
+        .collect()?;
+    assert_eq!(out.shape(), (0, 3));
+    Ok(())
+}