| /* |
| * 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.pig.quantiles; |
| |
| import java.io.IOException; |
| import java.util.Comparator; |
| |
| import org.apache.pig.EvalFunc; |
| import org.apache.pig.data.DataByteArray; |
| import org.apache.pig.data.Tuple; |
| |
| import com.yahoo.memory.Memory; |
| import com.yahoo.sketches.ArrayOfStringsSerDe; |
| import com.yahoo.sketches.quantiles.ItemsSketch; |
| |
| /** |
| * This UDF is to get a quantile value from an ItemsSketch<String>. 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, the 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). |
| */ |
| public class GetQuantileFromStringsSketch extends EvalFunc<String> { |
| |
| @Override |
| public String exec(final Tuple input) throws IOException { |
| if (input.size() != 2) { |
| throw new IllegalArgumentException("expected two inputs: sketch and fraction"); |
| } |
| |
| if (!(input.get(0) instanceof DataByteArray)) { |
| throw new IllegalArgumentException( |
| "expected a DataByteArray as a sketch, got " + input.get(0).getClass().getSimpleName()); |
| } |
| final DataByteArray dba = (DataByteArray) input.get(0); |
| final ItemsSketch<String> sketch = ItemsSketch.getInstance( |
| Memory.wrap(dba.get()), Comparator.naturalOrder(), new ArrayOfStringsSerDe()); |
| |
| if (!(input.get(1) instanceof Double)) { |
| throw new IllegalArgumentException( |
| "expected a double value as a fraction, got " + input.get(1).getClass().getSimpleName()); |
| } |
| final double fraction = (double) input.get(1); |
| return sketch.getQuantile(fraction); |
| } |
| |
| } |