[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1720: Implementation string concat

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

HaoYang670 commented on code in PR #1720:
URL: https://github.com/apache/arrow-rs/pull/1720#discussion_r878852329


##########
arrow/src/compute/kernels/concat.rs:
##########
@@ -102,6 +102,25 @@ pub fn concat(arrays: &[&dyn Array]) -> Result<ArrayRef> {
     Ok(make_array(mutable.freeze()))
 }
 
+// Elementwise concatenation of StringArrays
+pub fn string_concat<Offset: OffsetSizeTrait>(

Review Comment:
   I agree with @tustvold to create a new compute kernel. Also, list, binary, fixed size list and fix size binary can all be supported.



##########
arrow/src/compute/kernels/concat.rs:
##########
@@ -102,6 +102,25 @@ pub fn concat(arrays: &[&dyn Array]) -> Result<ArrayRef> {
     Ok(make_array(mutable.freeze()))
 }
 
+// Elementwise concatenation of StringArrays
+pub fn string_concat<Offset: OffsetSizeTrait>(

Review Comment:
   Maybe we should support concatenate arbitrary number of arrays. We could file a follow-on issue to track it.



##########
arrow/src/compute/kernels/concat.rs:
##########
@@ -102,6 +102,25 @@ 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>> {
+    let left_bitmap = left.data().null_bitmap().unwrap();
+    let right_bitmap = right.data().null_bitmap().unwrap();
+    let concat_bitmap = (left_bitmap & right_bitmap).unwrap();
+    Ok((0..left.len().max(right.len()))
+        .map(|i| {
+            if concat_bitmap.is_set(i) {
+                Some(left.value(i).to_owned() + right.value(i))
+            } else {
+                None
+            }
+        })
+        .collect::<GenericStringArray<Offset>>())

Review Comment:
   We could file a follow-on issue to add benchmarks.



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