Add NullState::is_valid and NullState::is_null

datafusion/physical-expr-common/src/aggregate/groups_accumulator/accumulate.rs

@@ -324,6 +324,18 @@ impl NullState {
         }
     }
 
+    /// Check if the accumulated value for the group at the given `index` is valid,
+    /// meaning that there was at least one value passing the filter for this group.
+    pub fn is_valid(&self, index: usize) -> bool {
+        self.seen_values.get_bit(index)
+    }
+
+    /// Check if the accumulated value for the group at the given `index` is `null`,
+    /// meaning that no values passing the filter were seen yet for this group.
+    pub fn is_null(&self, index: usize) -> bool {
+        !self.is_valid(index)
+    }
+
     /// Creates the a [`NullBuffer`] representing which group_indices
     /// should have null values (because they never saw any values)
     /// for the `emit_to` rows.
@@ -828,9 +840,12 @@ mod test {
 
             // Validate the final buffer (one value per group)
             let expected_null_buffer = mock.expected_null_buffer(total_num_groups);
+            for (i, expected) in expected_null_buffer.iter().enumerate() {
+                assert_eq!(expected, null_state.is_valid(i));
+                assert_eq!(!expected, null_state.is_null(i))
+            }
 
             let null_buffer = null_state.build(EmitTo::All);
-
             assert_eq!(null_buffer, expected_null_buffer);
         }
     }