HLLSketch to support String[] as produced by transformationSpec

[gipeshka]

Description

Current implementation of HllSketchBuildAggregator already supports List<String>, therefore it works fine with multi-value fields when building an aggregate. It would be nice if the aggregator would support String[] as well.

Motivation

What I tried was a following ingestion spec:

"dataSchema": {
  "transformSpec": {
    "transforms": [
      {
        "type": "expression",
        "name": "all_hashes",
        "expression": "array_concat(hashes_column_1, hashes_column_2)"
      }
    ]
  },
  "metricsSpec": [
    {
      "type": "HLLSketchBuild",
      "name": "hashes_sketch",
      "fieldName": "all_hashes"
    }
  ]
}

Which resulted in an error

org.apache.druid.java.util.common.IAE: Unsupported type class [Ljava.lang.String;
	at org.apache.druid.query.aggregation.datasketches.hll.HllSketchBuildAggregator.updateSketch(HllSketchBuildAggregator.java:119) ~[?:?]

Supposedly required change can be applied to HllSketchBuildAggregator as follows:

} else if (value instanceof String[]) {
      // noinspection unchecked
      String[] array = ((String[]) value);

      for (String s : array) {
        sketch.update(s.toCharArray());
      }

Just like it is currently done to List<String>

[gianm]

@gipeshka Would you be interested in doing a PR with this change? (And a test for it?)

[gipeshka]

@gianm yes, sure. Will do

[stale]

This issue has been marked as stale due to 280 days of inactivity. It will be closed in 4 weeks if no further activity occurs. If this issue is still relevant, please simply write any comment. Even if closed, you can still revive the issue at any time or discuss it on the dev@druid.apache.org list. Thank you for your contributions.

[stale]

This issue has been closed due to lack of activity. If you think that is incorrect, or the issue requires additional review, you can revive the issue at any time.