[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1787: Arbitrary size concat elements utf8

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

HaoYang670 commented on code in PR #1787:
URL: https://github.com/apache/arrow-rs/pull/1787#discussion_r893264207


##########
arrow/src/compute/kernels/concat_elements.rs:
##########
@@ -29,54 +29,76 @@ use crate::error::{ArrowError, Result};
 ///
 ///   ["Hello"] + ["World"] = ["HelloWorld"]
 ///
-///   ["a", "b"] + [None, "c"] = [None, "bc"]
+///   ["a", "b"] + [None, "c"] + [None, "d"] = [None, "bcd"]
 /// ```
 ///
-/// An error will be returned if `left` and `right` have different lengths
+/// An error will be returned if the [`StringArray`] are of different lengths.
 pub fn concat_elements_utf8<Offset: OffsetSizeTrait>(
-    left: &GenericStringArray<Offset>,
-    right: &GenericStringArray<Offset>,
+    arrays: &[&GenericStringArray<Offset>],
 ) -> Result<GenericStringArray<Offset>> {
-    if left.len() != right.len() {
+    if arrays.len() < 2 {

Review Comment:
   We should follow the pattern in `concat` kernel: https://github.com/apache/arrow-rs/blob/master/arrow/src/compute/kernels/concat.rs#L53-L61
   
   If you prefer FP style, you could write like this (not tested): 
   ```rust
   match array {
       [] => Err(...),
       [arr] => Ok((arr.slice(0, arr.len())),
       [arr, ..] => {// your code here},
   }
   ```



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