CODEWITHSUNDEEP
hadoopmapreduceapache-pig
rretzbach
rretzbach

Reputation: 744

Pig Mapreduce to count letters in a row

Instead of counting words I need to count letters. But I have problems implementing this using Apache Pig version 0.8.1-cdh3u1

Given the following input:

989;850;abcccc
29;395;aabbcc

The ouput should be:

989;850;a;1
989;850;b;1
989;850;c;4
29;395;a;2
29;395;b;2
29;395;c;2

Here is what I tried:

A = LOAD 'input' using PigStorage(';') as (x:int, y:int, content:chararray);
B = foreach A generate x, y, FLATTEN(STRSPLIT(content, '(?<=.)(?=.)', 6)) as letters;
C = foreach B generate x, y, FLATTEN(TOBAG(*)) as letters;
D = foreach C generate x, y, letters.letters as letter;
E = GROUP D BY (x,y,letter);
F = foreach E generate group.x as x, group.y as y, group.letter as letter, COUNT(D.letter) as count;

A, B and C can be dumped, but "dump D" results in "ERROR 2997: Unable to recreate exception from backed error: java.lang.ClassCastException: java.lang.Integer cannot be cast to org.apache.pig.data.Tuple"

dump C displays(despite the third value being a weird tuple):

(989,850,a)
(989,850,b)
(989,850,c)
(989,850,c)
(989,850,c)
(989,850,c)
(29,395,a)
(29,395,a)
(29,395,b)
(29,395,b)
(29,395,c)
(29,395,c)

Here are the schemas:

grunt> describe A; describe B; describe C; describe D; describe E; describe F;
A: {x: int,y: int,content: chararray}
B: {x: int,y: int,letters: bytearray}
C: {x: int,y: int,letters: (x: int,y: int,letters: bytearray)}
D: {x: int,y: int,letter: bytearray}
E: {group: (x: int,y: int,letter: bytearray),D: {x: int,y: int,letter: bytearray}}
F: {x: int,y: int,letter: bytearray,count: long}

This pig version doesn't seem to support TOBAG($2..$8), hence the TOBAG(*) which also includes x and y, but that could be sorted out synactically later... I'd like to avoid writing a UDF, otherwise I'd simply use the Java API directly.

But I don't really get the cast error. Can someone please explain it.

Upvotes: 1

Views: 3108

Answers (3)

user1594999
user1594999

Reputation: 1

You can try this

grunt> a = load 'inputfile.txt' using PigStorage(';') as (c1:chararray, c2:chararray, c3:chararray);
grunt> b = foreach a generate c1,c2,FLATTEN(TOKENIZE(REPLACE(c3,'','^'),'^')) as split_char;
grunt> c = group b by (c1,c2,split_char);
grunt> d = foreach c generate group, COUNT(b);
grunt> dump d;

Output looks like this:

((29,395,a),2)
((29,395,b),2)
((29,395,c),2)
((989,850,a),1)
((989,850,b),1)
((989,850,c),4)

Upvotes: 0

alexeipab
alexeipab

Reputation: 3619

I do not have 0.8 version, but could you try this one:

A = LOAD 'input' using PigStorage(';') as (x:int, y:int, content:chararray);
B = foreach A generate x, y, FLATTEN(STRSPLIT(content, '(?<=.)(?=.)', 6));
C = foreach B generate $0 as x, $1 as y, FLATTEN(TOBAG(*)) as letter;
E = GROUP C BY (x,y,letter);
F = foreach E generate group.x as x, group.y as y, group.letter as letter, COUNT(C.letter) as count;

Upvotes: 0

Lorand Bendig
Lorand Bendig

Reputation: 10650

I'd propose writing a custom UDF instead. A quick, raw implementation would look like this:

package com.example;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import org.apache.pig.EvalFunc;
import org.apache.pig.data.BagFactory;
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;

public class CharacterCount extends EvalFunc<DataBag> {

    private static final BagFactory bagFactory = BagFactory.getInstance();
    private static final TupleFactory tupleFactory = TupleFactory.getInstance();

    @Override
    public DataBag exec(Tuple input) throws IOException {
        try {

            Map<Character, Integer> charMap = new HashMap<Character, Integer>();

            DataBag result = bagFactory.newDefaultBag();
            int x = (Integer) input.get(0);
            int y = (Integer) input.get(1);
            String content = (String) input.get(2);

            for (int i = 0; i < content.length(); i++){
                char c = content.charAt(i);        
                Integer count = charMap.get(c);
                count = (count == null) ? 1 : count + 1;
                charMap.put(c, count);
            }

            for (Map.Entry<Character, Integer> entry : charMap.entrySet()) {
                Tuple res = tupleFactory.newTuple(4);
                res.set(0, x);
                res.set(1, y);
                res.set(2, String.valueOf(entry.getKey()));
                res.set(3, entry.getValue());
                result.add(res);
            }

            return result;

        } catch (Exception e) {
            throw new RuntimeException("CharacterCount error", e);
        }
    }

}

Pack it in a jar and execute it:

register '/home/user/test/myjar.jar';
A = LOAD '/user/hadoop/store/sample/charcount.txt' using PigStorage(';') 
      as (x:int, y:int, content:chararray);

B = foreach A generate flatten(com.example.CharacterCount(x,y,content)) 
      as (x:int, y:int, letter:chararray, count:int);

dump B;
(989,850,b,1)
(989,850,c,4)
(989,850,a,1)
(29,395,b,2)
(29,395,c,2)
(29,395,a,2)

Upvotes: 1

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