fix duration filters with different time units (#3179)

polars/polars-core/src/series/arithmetic.rs

@@ -345,7 +345,8 @@ pub(crate) fn coerce_lhs_rhs<'a>(
     Ok((left, right))
 }
 
-// Handle (Date | Datetime) +/- (Duration) | (Duration) +/- (Date | Datetime)
+// Handle (Date | Datetime) +/- (Duration) | (Duration) +/- (Date | Datetime) | (Duration) +-
+// (Duration)
 // Time arithmetic is only implemented on the date / datetime so ensure that's on left
 
 fn coerce_time_units<'a>(
@@ -365,6 +366,19 @@ fn coerce_time_units<'a>(
             Cow::Owned(rhs.cast(&DataType::Duration(units))?)
         };
         Ok((left, right))
+    } else if let (DataType::Duration(lu), DataType::Duration(ru)) = (lhs.dtype(), rhs.dtype()) {
+        let units = get_time_units(lu, ru);
+        let left = if *lu == units {
+            Cow::Borrowed(lhs)
+        } else {
+            Cow::Owned(lhs.cast(&DataType::Duration(units))?)
+        };
+        let right = if *ru == units {
+            Cow::Borrowed(rhs)
+        } else {
+            Cow::Owned(rhs.cast(&DataType::Duration(units))?)
+        };
+        Ok((left, right))
     } else if let (DataType::Date, DataType::Duration(units)) = (lhs.dtype(), rhs.dtype()) {
         let left = Cow::Owned(lhs.cast(&DataType::Datetime(*units, None))?);
         Ok((left, Cow::Borrowed(rhs)))

py-polars/tests/test_datelike.py

@@ -815,3 +815,15 @@ def test_timelike_init() -> None:
     for ts in [durations, dates, datetimes]:
         s = pl.Series(ts)
         assert s.to_list() == ts
+
+
+def test_duration_filter() -> None:
+    date_df = pl.DataFrame(
+        {
+            "start_date": [date(2022, 1, 1), date(2022, 1, 1), date(2022, 1, 1)],
+            "end_date": [date(2022, 1, 7), date(2022, 2, 20), date(2023, 1, 1)],
+        }
+    ).with_column((pl.col("end_date") - pl.col("start_date")).alias("time_passed"))
+
+    assert date_df.filter(pl.col("time_passed") < timedelta(days=30)).shape[0] == 1
+    assert date_df.filter(pl.col("time_passed") >= timedelta(days=30)).shape[0] == 2