| /* |
| * 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 "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.pig.builtin; |
| |
| import static java.lang.String.format; |
| |
| import java.io.IOException; |
| import java.util.HashSet; |
| import java.util.Iterator; |
| import java.util.Set; |
| |
| import org.apache.pig.EvalFunc; |
| import org.apache.pig.backend.executionengine.ExecException; |
| import org.apache.pig.data.BagFactory; |
| import org.apache.pig.data.DataBag; |
| import org.apache.pig.data.Tuple; |
| |
| /** |
| * SUBTRACT takes two bags as arguments and returns a new bag composed of tuples of first bag not in the second bag.<br> |
| * If null, bag arguments are replaced by empty bags. |
| * <p> |
| * The implementation assumes that both bags being passed to this function will fit entirely into memory simultaneously. |
| * </br> |
| * If that is not the case the UDF will still function, but it will be <strong>very</strong> slow. |
| */ |
| public class SUBTRACT extends EvalFunc<DataBag> { |
| |
| /** |
| * Compares the two bag fields from input Tuple and returns a new bag composed of elements of first bag not in the second bag. |
| * @param input a tuple with exactly two bag fields. |
| * @throws IOException if there are not exactly two fields in a tuple or if they are not {@link DataBag}. |
| */ |
| @Override |
| public DataBag exec(Tuple input) throws IOException { |
| if (input.size() != 2) { |
| throw new ExecException("SUBTRACT expected two inputs but received " + input.size() + " inputs."); |
| } |
| DataBag bag1 = toDataBag(input.get(0)); |
| DataBag bag2 = toDataBag(input.get(1)); |
| return subtract(bag1, bag2); |
| } |
| |
| private static String classNameOf(Object o) { |
| return o == null ? "null" : o.getClass().getSimpleName(); |
| } |
| |
| private static DataBag toDataBag(Object o) throws ExecException { |
| if (o == null) { |
| return BagFactory.getInstance().newDefaultBag(); |
| } |
| if (o instanceof DataBag) { |
| return (DataBag) o; |
| } |
| throw new ExecException(format("Expecting input to be DataBag only but was '%s'", classNameOf(o))); |
| } |
| |
| private static DataBag subtract(DataBag bag1, DataBag bag2) { |
| DataBag subtractBag2FromBag1 = BagFactory.getInstance().newDefaultBag(); |
| // convert each bag to Set, this does make the assumption that the sets will fit in memory. |
| Set<Tuple> set1 = toSet(bag1); |
| // remove elements of bag2 from set1 |
| Iterator<Tuple> bag2Iterator = bag2.iterator(); |
| while (bag2Iterator.hasNext()) { |
| set1.remove(bag2Iterator.next()); |
| } |
| // set1 now contains all elements of bag1 not in bag2 => we can build the resulting DataBag. |
| for (Tuple tuple : set1) { |
| subtractBag2FromBag1.add(tuple); |
| } |
| return subtractBag2FromBag1; |
| } |
| |
| private static Set<Tuple> toSet(DataBag bag) { |
| Set<Tuple> set = new HashSet<Tuple>(); |
| Iterator<Tuple> iterator = bag.iterator(); |
| while (iterator.hasNext()) { |
| set.add(iterator.next()); |
| } |
| return set; |
| } |
| |
| @Override |
| public boolean allowCompileTimeCalculation() { |
| return true; |
| } |
| } |