StringMin.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 "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 java.io.IOException;
import java.util.Iterator;

import org.apache.pig.Accumulator;
import org.apache.pig.Algebraic;
import org.apache.pig.EvalFunc;
import org.apache.pig.PigException;
import org.apache.pig.backend.executionengine.ExecException;
import org.apache.pig.data.DataBag;
import org.apache.pig.data.DataType;
import org.apache.pig.data.Tuple;
import org.apache.pig.data.TupleFactory;
import org.apache.pig.impl.logicalLayer.schema.Schema;


/**
 * This method should never be used directly, use {@link MIN}.
 */
public class StringMin extends EvalFunc<String> implements Algebraic, Accumulator<String> {

    @Override
    public String exec(Tuple input) throws IOException {
        try {
            return min(input);
        } catch (ExecException ee) {
            throw ee;
        }
    }

    public String getInitial() {
        return Initial.class.getName();
    }

    public String getIntermed() {
        return Intermediate.class.getName();
    }

    public String getFinal() {
        return Final.class.getName();
    }

    static public class Initial extends EvalFunc<Tuple> {
        private static TupleFactory tfact = TupleFactory.getInstance();

        @Override
        public Tuple exec(Tuple input) throws IOException {
            try {
                // input is a bag with one tuple containing
                // the column we are trying to min on
                DataBag bg = (DataBag) input.get(0);
                String s = null;
                if(bg.iterator().hasNext()) {
                    Tuple tp = bg.iterator().next();
                    s = (String)(tp.get(0));
                }
                return tfact.newTuple(s);
            } catch (ExecException ee) {
                throw ee;
            } catch (Exception e) {
                int errCode = 2106;
                String msg = "Error while computing min in " + this.getClass().getSimpleName();
                throw new ExecException(msg, errCode, PigException.BUG, e);           
            }
        }
    }

    static public class Intermediate extends EvalFunc<Tuple> {
        private static TupleFactory tfact = TupleFactory.getInstance();

        @Override
        public Tuple exec(Tuple input) throws IOException {
            try {
                return tfact.newTuple(min(input));
            } catch (ExecException ee) {
                throw ee;
            } catch (Exception e) {
                int errCode = 2106;
                String msg = "Error while computing min in " + this.getClass().getSimpleName();
                throw new ExecException(msg, errCode, PigException.BUG, e);           
            }
        }
    }
    static public class Final extends EvalFunc<String> {
        @Override
        public String exec(Tuple input) throws IOException {
            try {
                return min(input);
            } catch (ExecException ee) {
                throw ee;
            } catch (Exception e) {
                int errCode = 2106;
                String msg = "Error while computing min in " + this.getClass().getSimpleName();
                throw new ExecException(msg, errCode, PigException.BUG, e);           
            }
        }
    }

    static protected String min(Tuple input) throws ExecException {
        DataBag values = (DataBag)input.get(0);
        
        // if we were handed an empty bag, return NULL
        // this is in compliance with SQL standard
        if(values.size() == 0) {
            return null;
        }

        Iterator<Tuple> it = values.iterator();
        // assign first non null element as min to begin with
        String curMin = null;
        while(curMin == null && it.hasNext()) {
            Tuple t = it.next();
            curMin = (String)(t.get(0));
        }
        
        for (; it.hasNext();) {
            Tuple t = it.next();
            try {
                String s = (String)(t.get(0));
                if (s == null) continue;
                if( s.compareTo(curMin) < 0) {
                    curMin = s;
                }
                
            } catch (RuntimeException exp) {
                int errCode = 2103;
                String msg = "Problem while computing min of strings.";
                throw new ExecException(msg, errCode, PigException.BUG, exp);
            }
        }
    
        return curMin;
    }

    @Override
    public Schema outputSchema(Schema input) {
        return new Schema(new Schema.FieldSchema(null, DataType.CHARARRAY)); 
    }
    
    /* accumulator interface */
    private String intermediateMin = null;
    
    @Override
    public void accumulate(Tuple b) throws IOException {
        try {
            String curMin = min(b);
            if (curMin == null) {
                return;
            }
            // check if it lexicographically follows curMax
            if (intermediateMin == null || intermediateMin.compareTo(curMin) < 0) {
                intermediateMin = curMin;
            }            

        } catch (ExecException ee) {
            throw ee;
        } catch (Exception e) {
            int errCode = 2106;
            String msg = "Error while computing max in " + this.getClass().getSimpleName();
            throw new ExecException(msg, errCode, PigException.BUG, e);           
        }
    }

    @Override
    public void cleanup() {
        intermediateMin = null;
    }

    @Override
    public String getValue() {
        return intermediateMin;
    }

}