[GitHub] [arrow-rs] tustvold commented on a diff in pull request #2105: add test for skip_values in DictionaryDecoder and fix it

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

tustvold commented on code in PR #2105:
URL: https://github.com/apache/arrow-rs/pull/2105#discussion_r925664635


##########
parquet/src/arrow/array_reader/byte_array_dictionary.rs:
##########
@@ -476,6 +477,68 @@ mod tests {
         )
     }
 
+    #[test]
+    fn test_dictionary_preservation_skip() {
+        let data_type = utf8_dictionary();
+
+        let data: Vec<_> = vec!["0", "1", "0", "1", "2", "1", "2"]
+            .into_iter()
+            .map(ByteArray::from)
+            .collect();
+        let (dict, encoded) = encode_dictionary(&data);
+
+        let column_desc = utf8_column();
+        let mut decoder = DictionaryDecoder::<i32, i32>::new(&column_desc);
+
+        decoder
+            .set_dict(dict, 3, Encoding::RLE_DICTIONARY, false)
+            .unwrap();
+
+        decoder
+            .set_data(Encoding::RLE_DICTIONARY, encoded, 7, Some(data.len()))
+            .unwrap();
+
+        let mut output = DictionaryBuffer::<i32, i32>::default();
+
+        // read two skip one
+        assert_eq!(decoder.read(&mut output, 0..2).unwrap(), 2);
+        assert_eq!(decoder.skip_values(1).unwrap(), 1);
+
+        assert!(matches!(output, DictionaryBuffer::Dict { .. }));
+
+        // read two skip one
+        assert_eq!(decoder.read(&mut output, 2..4).unwrap(), 2);
+        assert_eq!(decoder.skip_values(1).unwrap(), 1);
+
+        // read one and test on skip at the end
+        assert_eq!(decoder.read(&mut output, 4..5).unwrap(), 1);
+        assert_eq!(decoder.skip_values(4).unwrap(), 0);
+
+        let valid = vec![true, true, true, true, true];
+        let valid_buffer = Buffer::from_iter(valid.iter().cloned());
+        output.pad_nulls(0, 5, 5, valid_buffer.as_slice());

Review Comment:
   Yes, call `BufferQueue::set_len`, which is what RecordReader will do



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