Add array_empty (#931)

Author: kosiew

docs/source/user-guide/common-operations/expressions.rst

@@ -77,12 +77,25 @@ approaches.
     df = ctx.from_pydict({"a": [[1, 2, 3], [4, 5, 6]]})
     df.select(col("a")[0].alias("a0"))
 
-
 .. warning::
 
     Indexing an element of an array via ``[]`` starts at index 0 whereas
     :py:func:`~datafusion.functions.array_element` starts at index 1.
 
+To check if an array is empty, you can use the function :py:func:`datafusion.functions.array_empty`.
+This function returns a boolean indicating whether the array is empty.
+
+.. ipython:: python
+
+    from datafusion import SessionContext, col
+    from datafusion.functions import array_empty
+
+    ctx = SessionContext()
+    df = ctx.from_pydict({"a": [[], [1, 2, 3]]})
+    df.select(array_empty(col("a")).alias("is_empty"))
+
+In this example, the `is_empty` column will contain `True` for the first row and `False` for the second row.
+
 Structs
 -------
 

python/datafusion/functions.py

@@ -51,6 +51,7 @@
     "array_dims",
     "array_distinct",
     "array_element",
+    "array_empty",
     "array_except",
     "array_extract",
     "array_has",
@@ -1160,6 +1161,11 @@ def array_element(array: Expr, n: Expr) -> Expr:
     return Expr(f.array_element(array.expr, n.expr))
 
 
+def array_empty(array: Expr) -> Expr:
+    """Returns a boolean indicating whether the array is empty."""
+    return Expr(f.array_empty(array.expr))
+
+
 def array_extract(array: Expr, n: Expr) -> Expr:
     """Extracts the element with the index n from the array.
 

python/tests/test_functions.py

@@ -309,6 +309,10 @@ def py_flatten(arr):
             lambda col: f.array_element(col, literal(1)),
             lambda data: [r[0] for r in data],
         ],
+        [
+            lambda col: f.array_empty(col),
+            lambda data: [len(r) == 0 for r in data],
+        ],
         [
             lambda col: f.array_extract(col, literal(1)),
             lambda data: [r[0] for r in data],

src/functions.rs

@@ -572,6 +572,7 @@ array_fn!(array_to_string, array delimiter);
 array_fn!(array_dims, array);
 array_fn!(array_distinct, array);
 array_fn!(array_element, array element);
+array_fn!(array_empty, array);
 array_fn!(array_length, array);
 array_fn!(array_has, first_array second_array);
 array_fn!(array_has_all, first_array second_array);
@@ -1003,6 +1004,7 @@ pub(crate) fn init_module(m: &Bound<'_, PyModule>) -> PyResult<()> {
     m.add_wrapped(wrap_pyfunction!(array_dims))?;
     m.add_wrapped(wrap_pyfunction!(array_distinct))?;
     m.add_wrapped(wrap_pyfunction!(array_element))?;
+    m.add_wrapped(wrap_pyfunction!(array_empty))?;
     m.add_wrapped(wrap_pyfunction!(array_length))?;
     m.add_wrapped(wrap_pyfunction!(array_has))?;
     m.add_wrapped(wrap_pyfunction!(array_has_all))?;