src/main/java/org/apache/datasketches/hive/quantiles/GetQuantileFromStringsSketchUDF.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
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 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
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package org.apache.datasketches.hive.quantiles;

import java.util.Comparator;

import org.apache.datasketches.ArrayOfStringsSerDe;
import org.apache.datasketches.memory.Memory;
import org.apache.datasketches.quantiles.ItemsSketch;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.BytesWritable;

@Description(name = "GetQuantile", value = "_FUNC_(sketch, fraction)",
    extended = " Returns a quantile value from a given ItemsSketch<String> sketch."
    + " A single value for a given fraction is returned."
    + " The fraction represents a normalized rank, and must be from 0 to 1 inclusive."
    + " For example, a fraction of 0.5 corresponds to 50th percentile, which is"
    + " the median value of the distribution (the number separating the higher half"
    + " of the probability distribution from the lower half).")
@SuppressWarnings("javadoc")
public class GetQuantileFromStringsSketchUDF extends UDF {

  /**
   * Returns a quantile value from a given sketch
   * @param serializedSketch serialized sketch
   * @param fraction value from 0 to 1 inclusive
   * @return quantile value
   */
  public String evaluate(final BytesWritable serializedSketch, final double fraction) {
    if (serializedSketch == null) { return null; }
    final ItemsSketch<String> sketch = ItemsSketch.getInstance(
      Memory.wrap(serializedSketch.getBytes()),
      Comparator.naturalOrder(),
      new ArrayOfStringsSerDe()
    );
    return sketch.getQuantile(fraction);
  }

}