[FEAT] Add basic list aggregations

daft/daft.pyi

@@ -943,8 +943,12 @@ class PyExpr:
     def image_resize(self, w: int, h: int) -> PyExpr: ...
     def image_crop(self, bbox: PyExpr) -> PyExpr: ...
     def list_join(self, delimiter: PyExpr) -> PyExpr: ...
-    def list_lengths(self) -> PyExpr: ...
+    def list_count(self, mode: CountMode) -> PyExpr: ...
     def list_get(self, idx: PyExpr, default: PyExpr) -> PyExpr: ...
+    def list_sum(self) -> PyExpr: ...
+    def list_mean(self) -> PyExpr: ...
+    def list_min(self) -> PyExpr: ...
+    def list_max(self) -> PyExpr: ...
     def struct_get(self, name: str) -> PyExpr: ...
     def url_download(
         self, max_connections: int, raise_error_on_failure: bool, multi_thread: bool, config: IOConfig
@@ -1037,7 +1041,7 @@ class PySeries:
     def partitioning_years(self) -> PySeries: ...
     def partitioning_iceberg_bucket(self, n: int) -> PySeries: ...
     def partitioning_iceberg_truncate(self, w: int) -> PySeries: ...
-    def list_lengths(self) -> PySeries: ...
+    def list_count(self, mode: CountMode) -> PySeries: ...
     def list_get(self, idx: PySeries, default: PySeries) -> PySeries: ...
     def image_decode(self) -> PySeries: ...
     def image_encode(self, image_format: ImageFormat) -> PySeries: ...

daft/expressions/expressions.py

@@ -868,13 +868,24 @@ def join(self, delimiter: str | Expression) -> Expression:
         delimiter_expr = Expression._to_expression(delimiter)
         return Expression._from_pyexpr(self._expr.list_join(delimiter_expr._expr))
 
+    def count(self, mode: CountMode = CountMode.Valid) -> Expression:
+        """Counts the number of elements in each list
+
+        Args:
+            mode: The mode to use for counting. Defaults to CountMode.Valid
+
+        Returns:
+            Expression: a UInt64 expression which is the length of each list
+        """
+        return Expression._from_pyexpr(self._expr.list_count(mode))
+
     def lengths(self) -> Expression:
         """Gets the length of each list
 
         Returns:
             Expression: a UInt64 expression which is the length of each list
         """
-        return Expression._from_pyexpr(self._expr.list_lengths())
+        return Expression._from_pyexpr(self._expr.list_count(CountMode.All))
 
     def get(self, idx: int | Expression, default: object = None) -> Expression:
         """Gets the element at an index in each list
@@ -890,6 +901,38 @@ def get(self, idx: int | Expression, default: object = None) -> Expression:
         default_expr = lit(default)
         return Expression._from_pyexpr(self._expr.list_get(idx_expr._expr, default_expr._expr))
 
+    def sum(self) -> Expression:
+        """Sums each list. Empty lists and lists with all nulls yield null.
+
+        Returns:
+            Expression: an expression with the type of the list values
+        """
+        return Expression._from_pyexpr(self._expr.list_sum())
+
+    def mean(self) -> Expression:
+        """Calculates the mean of each list. If no non-null values in a list, the result is null.
+
+        Returns:
+            Expression: a Float64 expression with the type of the list values
+        """
+        return Expression._from_pyexpr(self._expr.list_mean())
+
+    def min(self) -> Expression:
+        """Calculates the minimum of each list. If no non-null values in a list, the result is null.
+
+        Returns:
+            Expression: a Float64 expression with the type of the list values
+        """
+        return Expression._from_pyexpr(self._expr.list_min())
+
+    def max(self) -> Expression:
+        """Calculates the maximum of each list. If no non-null values in a list, the result is null.
+
+        Returns:
+            Expression: a Float64 expression with the type of the list values
+        """
+        return Expression._from_pyexpr(self._expr.list_max())
+
 
 class ExpressionStructNamespace(ExpressionNamespace):
     def get(self, name: str) -> Expression:

daft/series.py

@@ -666,7 +666,7 @@ def iceberg_truncate(self, w: int) -> Series:
 
 class SeriesListNamespace(SeriesNamespace):
     def lengths(self) -> Series:
-        return Series._from_pyseries(self._series.list_lengths())
+        return Series._from_pyseries(self._series.list_count(CountMode.All))
 
     def get(self, idx: Series, default: Series) -> Series:
         return Series._from_pyseries(self._series.list_get(idx._series, default._series))

src/daft-core/src/array/ops/count.rs

@@ -32,7 +32,7 @@ fn grouped_count_arrow_bitmap(
                 .iter()
                 .map(|g| {
                     g.iter()
-                        .map(|i| validity.get_bit(!*i as usize) as u64)
+                        .map(|i| !validity.get_bit(*i as usize) as u64)
                         .sum()
                 })
                 .collect(),