Feature: unsafe_get for ListArray of Numeric data types.

firebolt/arrays/base.mojo

@@ -84,7 +84,7 @@ struct ArrayData(Copyable, Movable, Representable, Stringable, Writable):
             if self.dtype.native == known_type:
                 writer.write(self.buffers[0][].unsafe_get[known_type](index))
                 return
-        writer.write("Can't process data type:")
+        writer.write("dtype=")
         writer.write(self.dtype)
 
     fn write_to[W: Writer](self, mut writer: W):

firebolt/arrays/nested.mojo

@@ -24,21 +24,31 @@ struct ListArray(Array):
         self.values = data.children[0]
         self.capacity = data.length
 
-    fn __init__[T: Array](out self, values: T, capacity: Int = 0):
-        var bitmap = Bitmap.alloc(capacity)
-        var offsets = Buffer.alloc[DType.uint32](capacity + 1)
-        offsets.unsafe_set[DType.uint32](0, 0)
+    fn __init__[T: Array](out self, var values: T, capacity: Int = 1):
+        """Initialize a list with the given values.
+
+        Default capacity is at least 1 to accomodate the values.
 
+        Args:
+            values: Array to use as the first element in the ListArray.
+            capacity: The capacity of the ListArray.
+        """
         var values_data = values.as_data()
         var list_dtype = list_(values_data.dtype)
 
+        var bitmap = Bitmap.alloc(capacity)
+        bitmap.unsafe_set(0, True)
+        var offsets = Buffer.alloc[DType.uint32](capacity + 1)
+        offsets.unsafe_set[DType.uint32](0, 0)
+        offsets.unsafe_set[DType.uint32](1, values_data.length)
+
         self.capacity = capacity
         self.bitmap = ArcPointer(bitmap^)
         self.offsets = ArcPointer(offsets^)
         self.values = ArcPointer(values_data^)
         self.data = ArrayData(
             dtype=list_dtype,
-            length=0,
+            length=1,
             bitmap=self.bitmap,
             buffers=List(self.offsets),
             children=List(self.values),
@@ -68,6 +78,27 @@ struct ListArray(Array):
         )
         self.data.length += 1
 
+    fn unsafe_get(self, index: Int) raises -> ArrayData:
+        """Access the value at a given index in the list array."""
+        var child_dtype = self.data.dtype.fields[0].dtype
+        if not child_dtype.is_numeric():
+            raise Error(
+                "Only numeric dtype supported right now, got {}".format(
+                    child_dtype
+                )
+            )
+        var start = Int(self.offsets[].unsafe_get[DType.int32](index))
+        var end = Int(self.offsets[].unsafe_get[DType.int32](index + 1))
+        ref first_child = self.data.children[0][]
+        return ArrayData(
+            dtype=child_dtype,
+            bitmap=first_child.bitmap,
+            buffers=first_child.buffers,
+            offset=self.data.offset + start,
+            length=end - start,
+            children=List[ArcPointer[ArrayData]](),
+        )
+
     fn write_to[W: Writer](self, mut writer: W):
         """
         Formats this ListArray to the provided Writer.

firebolt/arrays/tests/test_nested.mojo

@@ -7,14 +7,13 @@ from firebolt.test_fixtures.bool_array import as_bool_array_scalar
 
 
 def test_list_int_array():
-    var ints = Int64Array()
-    var lists = ListArray(ints)
-    assert_equal(lists.data.dtype, list_(int64))
-
+    var ints = Int64Array(capacity=3)
     ints.append(1)
     ints.append(2)
     ints.append(3)
-    lists.unsafe_append(True)
+    var lists = ListArray(ints^)
+    assert_equal(lists.data.dtype, list_(int64))
+
     assert_equal(len(lists), 1)
 
     var data = lists.as_data()
@@ -23,15 +22,18 @@ def test_list_int_array():
     var arr = data.as_list()
     assert_equal(len(arr), 1)
 
+    var first_value = lists.unsafe_get(0)
+    assert_equal(first_value.__str__().strip(), "1 2 3")
+
 
 def test_list_bool_array():
     var bools = BoolArray()
-    var lists = ListArray(bools)
 
     bools.append(as_bool_array_scalar(True))
     bools.append(as_bool_array_scalar(False))
     bools.append(as_bool_array_scalar(True))
-    lists.unsafe_append(True)
+
+    var lists = ListArray(bools^)
     assert_equal(len(lists), 1)
 
 
@@ -57,13 +59,13 @@ def test_struct_array():
 
 def test_list_array_str_repr():
     var ints = Int64Array()
-    var lists = ListArray(ints)
+    var lists = ListArray(ints^)
 
     var str_repr = lists.__str__()
     var repr_repr = lists.__repr__()
 
-    assert_equal(str_repr, "ListArray(length=0)")
-    assert_equal(repr_repr, "ListArray(length=0)")
+    assert_equal(str_repr, "ListArray(length=1)")
+    assert_equal(repr_repr, "ListArray(length=1)")
     assert_equal(str_repr, repr_repr)
 
 
@@ -81,3 +83,8 @@ def test_struct_array_str_repr():
     assert_equal(str_repr, "StructArray(length=0)")
     assert_equal(repr_repr, "StructArray(length=0)")
     assert_equal(str_repr, repr_repr)
+
+
+fn main() raises -> None:
+    """Main entry point to get stdout during testing."""
+    test_list_int_array()

firebolt/dtypes.mojo

@@ -300,6 +300,8 @@ struct DataType(
             writer.write("int32")
         elif self.code == INT64:
             writer.write("int64")
+        elif self.code == LIST:
+            writer.write("list")
         elif self.code == STRUCT:
             writer.write("struct")
         else: