[GitHub] [arrow-rs] Ismail-Maj commented on a diff in pull request #1720: Implementation string concat

[GitBox <gi...@apache.org>]

Ismail-Maj commented on code in PR #1720:
URL: https://github.com/apache/arrow-rs/pull/1720#discussion_r879213096


##########
arrow/src/compute/kernels/concat.rs:
##########
@@ -102,6 +102,72 @@ pub fn concat(arrays: &[&dyn Array]) -> Result<ArrayRef> {
     Ok(make_array(mutable.freeze()))
 }
 
+// Elementwise concatenation of StringArrays
+pub fn string_concat<Offset: OffsetSizeTrait>(
+    left: &GenericStringArray<Offset>,
+    right: &GenericStringArray<Offset>,
+) -> Result<GenericStringArray<Offset>> {
+    // TODO: Handle non-zero offset in source ArrayData
+
+    if left.len() != right.len() {
+        return Err(ArrowError::ComputeError(
+            "StringArrays must have the same length".to_string(),
+        ));
+    }
+
+    let output_bitmap = match (left.data().null_bitmap(), right.data().null_bitmap()) {
+        (Some(left_bitmap), Some(right_bitmap)) => Some((left_bitmap & right_bitmap)?),
+        (Some(left_bitmap), None) => Some(left_bitmap.clone()),
+        (None, Some(right_bitmap)) => Some(right_bitmap.clone()),
+        (None, None) => None,
+    };
+
+    let left_offsets = left.value_offsets();
+    let right_offsets = right.value_offsets();
+
+    let left_buffer = left.value_data();
+    let right_buffer = right.value_data();
+    let left_values = left_buffer.as_slice();
+    let right_values = right_buffer.as_slice();
+
+    let mut output_offsets = BufferBuilder::<Offset>::new(left_offsets.len());
+    let mut output_values =
+        BufferBuilder::<u8>::new(left_values.len() + right_values.len());
+
+    output_offsets.append(Offset::zero());
+    for (idx, (l, r)) in left_offsets
+        .windows(2)
+        .zip(right_offsets.windows(2))
+        .enumerate()
+    {
+        match &output_bitmap {
+            Some(bitmap) if { bitmap.is_set(idx) } => {

Review Comment:
   bug here, handle `None`



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