[GitHub] [arrow] jorgecarleitao commented on a change in pull request #8171: ARROW-9977: [Rust] Added min/max of [Large]StringArray

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

jorgecarleitao commented on a change in pull request #8171:
URL: https://github.com/apache/arrow/pull/8171#discussion_r487430955



##########
File path: rust/arrow/src/compute/kernels/aggregate.rs
##########
@@ -19,9 +19,42 @@
 
 use std::ops::Add;
 
-use crate::array::{Array, PrimitiveArray};
+use crate::array::{Array, LargeStringArray, PrimitiveArray, StringArray};
 use crate::datatypes::ArrowNumericType;
 
+/// Helper macro to perform min/max of strings
+macro_rules! min_max_string_helper {
+    ($array:expr, $cmp:tt) => {{
+        let null_count = $array.null_count();
+
+        if null_count == $array.len() {
+            return None
+        }
+        let mut n = "";
+        let mut has_value = false;
+        let data = $array.data();
+
+        if null_count == 0 {
+            for i in 0..data.len() {
+                let item = $array.value(i);
+                if !has_value || (&n $cmp &item) {
+                    has_value = true;
+                    n = item;
+                }
+            }
+        } else {
+            for i in 0..data.len() {
+                let item = $array.value(i);
+                if !has_value || data.is_valid(i) && (&n $cmp &item) {

Review comment:
       You are right. Amazing catch 💯💯.  I pushed a fix to it. This was also the case for primitive types, and so I also added a test and fix to them.




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