src/main/java/com/yahoo/sketches/hive/quantiles/GetQuantileFromStringsSketchUDF.java

/*
 * Copyright 2016, Yahoo! Inc.
 * Licensed under the terms of the Apache License 2.0. See LICENSE file at the project root for terms.
 */

package com.yahoo.sketches.hive.quantiles;

import java.util.Comparator;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.io.BytesWritable;

import com.yahoo.memory.Memory;
import com.yahoo.sketches.ArrayOfStringsSerDe;
import com.yahoo.sketches.quantiles.ItemsSketch;

@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);
  }

}