[GitHub] [arrow-rs] tustvold commented on a diff in pull request #2100: Support skip_values in DictionaryDecoder

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

tustvold commented on code in PR #2100:
URL: https://github.com/apache/arrow-rs/pull/2100#discussion_r923612719


##########
parquet/src/arrow/array_reader/byte_array_dictionary.rs:
##########
@@ -507,6 +519,51 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_dictionary_skip_fallback() {
+        let data_type = utf8_dictionary();
+        let data = vec!["hello", "world", "a", "b"];
+
+        let (pages, encoded_dictionary) = byte_array_all_encodings(data.clone());
+        let num_encodings = pages.len();
+
+        let column_desc = utf8_column();
+        let mut decoder = DictionaryDecoder::<i32, i32>::new(&column_desc);
+
+        decoder
+            .set_dict(encoded_dictionary, 4, Encoding::RLE_DICTIONARY, false)
+            .unwrap();
+
+        // Read all pages into single buffer
+        let mut output = DictionaryBuffer::<i32, i32>::default();
+
+        for (encoding, page) in pages {
+            decoder.set_data(encoding, page, 4, Some(4)).unwrap();
+            decoder.skip_values(2).expect("skipping two values");
+            assert_eq!(decoder.read(&mut output, 0..1024).unwrap(), 2);
+        }
+        let array = output.into_array(None, &data_type).unwrap();
+        assert_eq!(array.data_type(), &data_type);
+
+        let array = cast(&array, &ArrowType::Utf8).unwrap();
+        let strings = array.as_any().downcast_ref::<StringArray>().unwrap();
+        assert_eq!(strings.len(), (data.len() - 2) * num_encodings);
+
+        // Should have a copy of `data` for each encoding
+        for i in 0..num_encodings {
+            assert_eq!(
+                &strings
+                    .iter()
+                    .skip(i * (data.len() - 2))

Review Comment:
   ```suggestion
                       .skip(i * 2)
   ```



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