[GitHub] [arrow] jorgecarleitao commented on a change in pull request #8170: ARROW-9971: [Rust] Improve speed of `take` by 2x-3x (change scaling with batch size)

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

jorgecarleitao commented on a change in pull request #8170:
URL: https://github.com/apache/arrow/pull/8170#discussion_r487071953



##########
File path: rust/arrow/src/compute/kernels/take.rs
##########
@@ -425,22 +514,32 @@ mod tests {
     #[test]
     fn test_take_string() {
         let index = UInt32Array::from(vec![Some(3), None, Some(1), Some(3), Some(4)]);
-        let mut builder: StringBuilder = StringBuilder::new(6);
-        builder.append_value("one").unwrap();
-        builder.append_null().unwrap();
-        builder.append_value("three").unwrap();
-        builder.append_value("four").unwrap();
-        builder.append_value("five").unwrap();
-        let array = Arc::new(builder.finish()) as ArrayRef;
-        let a = take(&array, &index, None).unwrap();
-        assert_eq!(a.len(), index.len());
-        builder.append_value("four").unwrap();
-        builder.append_null().unwrap();
-        builder.append_null().unwrap();
-        builder.append_value("four").unwrap();
-        builder.append_value("five").unwrap();
-        let b = builder.finish();
-        assert_eq!(a.data(), b.data());
+
+        let array = StringArray::from(vec![
+            Some("one"),
+            None,
+            Some("three"),
+            Some("four"),
+            Some("five"),
+        ]);
+        let array = Arc::new(array) as ArrayRef;
+
+        let actual = take(&array, &index, None).unwrap();
+        assert_eq!(actual.len(), index.len());
+
+        let actual = actual.as_any().downcast_ref::<StringArray>().unwrap();
+
+        let expected =
+            StringArray::from(vec![Some("four"), None, None, Some("four"), Some("five")]);
+
+        for i in 0..index.len() {

Review comment:
       This test is semantically different(!). The new implementation takes all values, irrespetively of the nullabillity, which causes `data()` to be different. However, do take a critical view on this issue, please!




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