Add interleave kernel (apache#1523)

arrow/src/compute/kernels/interleave.rs

@@ -0,0 +1,201 @@
+use arrow_array::{make_array, new_empty_array, Array, ArrayRef};
+use arrow_data::transform::MutableArrayData;
+use arrow_schema::ArrowError;
+
+///
+/// Takes elements by index from an array of [`Array`], creating a new [`Array`] from those values.
+///
+/// Each element in `indices` is a pair of `usize` with the first identifying the index
+/// of the [`Array`] in `values`, and the second the index of the value within that [`Array`]
+///
+/// ```text
+/// ┌─────────────────┐      ┌─────────┐                                  ┌─────────────────┐
+/// │        A        │      │ (0, 0)  │        interleave(               │        A        │
+/// ├─────────────────┤      ├─────────┤          [values0, values1],     ├─────────────────┤
+/// │        D        │      │ (1, 0)  │          indices                 │        B        │
+/// └─────────────────┘      ├─────────┤        )                         ├─────────────────┤
+///   values array 0         │ (1, 1)  │      ─────────────────────────▶  │        C        │
+///                          ├─────────┤                                  ├─────────────────┤
+///                          │ (0, 1)  │                                  │        D        │
+///                          └─────────┘                                  └─────────────────┘
+/// ┌─────────────────┐       indices
+/// │        B        │        array
+/// ├─────────────────┤                                                    result
+/// │        C        │
+/// ├─────────────────┤
+/// │        E        │
+/// └─────────────────┘
+///   values array 1
+/// ```
+///
+/// For selecting values by index from a single array see [compute::take](crate::compute::take)
+///
+/// # Panics
+///
+/// Panics if the arrays do not have the same data type or `values` is empty
+pub fn interleave(
+    values: &[&dyn Array],
+    indices: &[(usize, usize)],
+) -> Result<ArrayRef, ArrowError> {
+    if values.is_empty() {
+        return Err(ArrowError::InvalidArgumentError(
+            "interleave requires input of at least one array".to_string(),
+        ));
+    }
+    let data_type = values[0].data_type();
+
+    if values
+        .iter()
+        .skip(1)
+        .any(|array| array.data_type() != data_type)
+    {
+        return Err(ArrowError::InvalidArgumentError(
+            "It is not possible to interleave arrays of different data types."
+                .to_string(),
+        ));
+    }
+
+    if indices.is_empty() {
+        return Ok(new_empty_array(data_type));
+    }
+
+    // TODO: Add specialized implementations (#1523)
+
+    interleave_fallback(values, indices)
+}
+
+/// Fallback implementation of interleave using [`MutableArrayData`]
+fn interleave_fallback(
+    values: &[&dyn Array],
+    indices: &[(usize, usize)],
+) -> Result<ArrayRef, ArrowError> {
+    let arrays: Vec<_> = values.iter().map(|x| x.data()).collect();
+    let mut array_data = MutableArrayData::new(arrays, false, indices.len());
+
+    let mut cur_array = indices[0].0;
+    let mut start_row_idx = indices[0].1;
+    let mut end_row_idx = start_row_idx + 1;
+
+    for (array, row) in indices.iter().skip(1).copied() {
+        if array == cur_array && row == end_row_idx {
+            // subsequent row in same batch
+            end_row_idx += 1;
+            continue;
+        }
+
+        // emit current batch of rows for current buffer
+        array_data.extend(cur_array, start_row_idx, end_row_idx);
+
+        // start new batch of rows
+        cur_array = array;
+        start_row_idx = row;
+        end_row_idx = start_row_idx + 1;
+    }
+
+    // emit final batch of rows
+    array_data.extend(cur_array, start_row_idx, end_row_idx);
+    Ok(make_array(array_data.freeze()))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use arrow_array::builder::{Int32Builder, ListBuilder};
+    use arrow_array::cast::{as_primitive_array, as_string_array};
+    use arrow_array::types::Int32Type;
+    use arrow_array::{Int32Array, ListArray, StringArray};
+
+    #[test]
+    fn test_primitive() {
+        let a = Int32Array::from_iter_values([1, 2, 3, 4]);
+        let b = Int32Array::from_iter_values([5, 6, 7]);
+        let c = Int32Array::from_iter_values([8, 9, 10]);
+        let values =
+            interleave(&[&a, &b, &c], &[(0, 3), (0, 3), (2, 2), (2, 0), (1, 1)]).unwrap();
+        let v = as_primitive_array::<Int32Type>(&values);
+        assert_eq!(v.values(), &[4, 4, 10, 8, 6]);
+    }
+
+    #[test]
+    fn test_primitive_nulls() {
+        let a = Int32Array::from_iter_values([1, 2, 3, 4]);
+        let b = Int32Array::from_iter([Some(1), Some(4), None]);
+        let values =
+            interleave(&[&a, &b], &[(0, 1), (1, 2), (1, 2), (0, 3), (0, 2)]).unwrap();
+        let v: Vec<_> = as_primitive_array::<Int32Type>(&values)
+            .into_iter()
+            .collect();
+        assert_eq!(&v, &[Some(2), None, None, Some(4), Some(3)])
+    }
+
+    #[test]
+    fn test_primitive_empty() {
+        let a = Int32Array::from_iter_values([1, 2, 3, 4]);
+        let v = interleave(&[&a], &[]).unwrap();
+        assert!(v.is_empty());
+    }
+
+    #[test]
+    fn test_strings() {
+        let a = StringArray::from_iter_values(["a", "b", "c"]);
+        let b = StringArray::from_iter_values(["hello", "world", "foo"]);
+        let values =
+            interleave(&[&a, &b], &[(0, 2), (0, 2), (1, 0), (1, 1), (0, 1)]).unwrap();
+        let v = as_string_array(&values);
+        let values: Vec<_> = v.into_iter().collect();
+        assert_eq!(
+            &values,
+            &[
+                Some("c"),
+                Some("c"),
+                Some("hello"),
+                Some("world"),
+                Some("b")
+            ]
+        )
+    }
+
+    #[test]
+    fn test_lists() {
+        // [[1, 2], null, [3]]
+        let mut a = ListBuilder::new(Int32Builder::new());
+        a.values().append_value(1);
+        a.values().append_value(2);
+        a.append(true);
+        a.append(false);
+        a.values().append_value(3);
+        a.append(true);
+        let a = a.finish();
+
+        // [[4], null, [5, 6, null]]
+        let mut b = ListBuilder::new(Int32Builder::new());
+        b.values().append_value(4);
+        b.append(true);
+        b.append(false);
+        b.values().append_value(5);
+        b.values().append_value(6);
+        b.values().append_null();
+        b.append(true);
+        let b = b.finish();
+
+        let values =
+            interleave(&[&a, &b], &[(0, 2), (0, 1), (1, 0), (1, 2), (1, 1)]).unwrap();
+        let v = values.as_any().downcast_ref::<ListArray>().unwrap();
+
+        // [[3], null, [4], [5, 6, null], null]
+        let mut expected = ListBuilder::new(Int32Builder::new());
+        expected.values().append_value(3);
+        expected.append(true);
+        expected.append(false);
+        expected.values().append_value(4);
+        expected.append(true);
+        expected.values().append_value(5);
+        expected.values().append_value(6);
+        expected.values().append_null();
+        expected.append(true);
+        expected.append(false);
+        let expected = expected.finish();
+
+        assert_eq!(v, &expected);
+    }
+}

arrow/src/compute/kernels/mod.rs

@@ -28,6 +28,7 @@ pub mod comparison;
 pub mod concat;
 pub mod concat_elements;
 pub mod filter;
+pub mod interleave;
 pub mod length;
 pub mod limit;
 pub mod partition;

arrow/src/compute/kernels/take.rs

@@ -46,15 +46,20 @@ use num::{ToPrimitive, Zero};
 /// ├─────────────────┤      └─────────┘                              └─────────────────┘
 /// │        E        │
 /// └─────────────────┘
-///    values array            indicies array                              result
+///    values array          indices array                              result
 /// ```
 ///
+/// For selecting values by index from multiple arrays see [compute::interleave](crate::compute::interleave)
+///
 /// # Errors
 /// This function errors whenever:
 /// * An index cannot be casted to `usize` (typically 32 bit architectures)
 /// * An index is out of bounds and `options` is set to check bounds.
+///
 /// # Safety
-/// When `options` is not set to check bounds (default), taking indexes after `len` is undefined behavior.
+///
+/// When `options` is not set to check bounds, taking indexes after `len` will panic.
+///
 /// # Examples
 /// ```
 /// use arrow::array::{StringArray, UInt32Array};

arrow/src/compute/mod.rs

@@ -29,6 +29,7 @@ pub use self::kernels::cast::*;
 pub use self::kernels::comparison::*;
 pub use self::kernels::concat::*;
 pub use self::kernels::filter::*;
+pub use self::kernels::interleave::*;
 pub use self::kernels::limit::*;
 pub use self::kernels::partition::*;
 pub use self::kernels::regexp::*;