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MapReduce, mail # user - Change the output of Reduce function


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Felipe Gutierrez 2013-07-25, 18:58
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Shahab Yunus 2013-07-25, 19:07
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Felipe Gutierrez 2013-07-25, 19:18
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Re: Change the output of Reduce function
Mohammad Tariq 2013-07-25, 19:26
Probably by that Shahab means that you can use NullWritable as your key
from the Reducer. If you do so your Reducer will just emit the value
without the key. Something like this :

output.collect(NullWritable.get(), new MyWritable(text));

Warm Regards,
Tariq
cloudfront.blogspot.com
On Fri, Jul 26, 2013 at 12:48 AM, Felipe Gutierrez <
[EMAIL PROTECTED]> wrote:

> Sorry, I think I didnt understand,
> Does NullWritable go to replate MyWritable? But this is may value. My key
> is a Text.
> Regards,
> Felipe
>
>
>
> On Thu, Jul 25, 2013 at 4:07 PM, Shahab Yunus <[EMAIL PROTECTED]>wrote:
>
>> I think uou can use NullWritable as key.
>>
>> http://hadoop.apache.org/docs/current/api/org/apache/hadoop/io/NullWritable.html
>>
>>
>> Regards,
>> Shahab
>>
>>
>> On Thu, Jul 25, 2013 at 2:58 PM, Felipe Gutierrez <
>> [EMAIL PROTECTED]> wrote:
>>
>>> I did a MapReduce program to execute a Grep function. I know there is a
>>> Grep function at hadoop examples, but I want to make my Grep MapReduce to
>>> explain to other.
>>> My problem is that my out put shows the key/value. I want to show only
>>> the value, since I saved the line number at this value. Example:
>>>
>>> 00048 [ line 6298 : Jul 25 15:18:14 felipe kernel: [ 2168.644689]
>>> wlan0: associated ]
>>>
>>> Here is my code. Thanks,
>>> Felipe
>>>
>>> package grep;
>>>
>>> import java.io.File;
>>> import java.io.FileReader;
>>> import java.io.LineNumberReader;
>>>
>>> import org.apache.hadoop.fs.Path;
>>> import org.apache.hadoop.io.Text;
>>> import org.apache.hadoop.mapred.FileInputFormat;
>>> import org.apache.hadoop.mapred.FileOutputFormat;
>>> import org.apache.hadoop.mapred.JobClient;
>>> import org.apache.hadoop.mapred.JobConf;
>>> import org.apache.hadoop.mapred.TextInputFormat;
>>> import org.apache.hadoop.mapred.TextOutputFormat;
>>>
>>> public class Main {
>>>
>>>  public static void main(String[] args) throws Exception {
>>>
>>> if (args == null || args.length != 3) {
>>>  System.err.println("Usage: Main <in> <out> <regex>");
>>> System.exit(-1);
>>>  }
>>>
>>> JobConf conf = new JobConf(Main.class);
>>> conf.setJobName("grep");
>>>
>>> String input = args[0];
>>> String output = args[1];
>>> String regex = args[2];
>>>
>>> File arquivoLeitura = new File(input);
>>> LineNumberReader linhaLeitura = new LineNumberReader(new FileReader(
>>>  arquivoLeitura));
>>> linhaLeitura.skip(arquivoLeitura.length());
>>> String lines = String.valueOf(linhaLeitura.getLineNumber() + 1);
>>>  conf.set("grep.regex", regex);
>>> conf.set("grep.lines", lines);
>>>
>>> conf.setOutputKeyClass(Text.class);
>>>  conf.setOutputValueClass(MyWritable.class);
>>>
>>> conf.setMapperClass(GrepMapper.class);
>>> conf.setCombinerClass(GrepReducer.class);
>>>  conf.setReducerClass(GrepReducer.class);
>>>
>>> conf.setInputFormat(TextInputFormat.class);
>>>  conf.setOutputFormat(TextOutputFormat.class);
>>>
>>> FileInputFormat.setInputPaths(conf, new Path(input));
>>>  FileOutputFormat.setOutputPath(conf, new Path(output));
>>>
>>> JobClient.runJob(conf);
>>> }
>>> }
>>>
>>> package grep;
>>>
>>> import java.io.IOException;
>>> import java.text.DecimalFormat;
>>>
>>> import org.apache.hadoop.io.LongWritable;
>>> import org.apache.hadoop.io.Text;
>>> import org.apache.hadoop.mapred.JobConf;
>>> import org.apache.hadoop.mapred.MapReduceBase;
>>> import org.apache.hadoop.mapred.Mapper;
>>> import org.apache.hadoop.mapred.OutputCollector;
>>> import org.apache.hadoop.mapred.Reporter;
>>>
>>> public class GrepMapper extends MapReduceBase implements
>>> Mapper<LongWritable, Text, Text, MyWritable> {
>>>
>>> private static long line = 1;
>>> private static long n = 0;
>>> private static long divisor = 1;
>>>  private static long qtdLines = 0;
>>> private Text k = new Text();
>>>
>>> public void map(LongWritable key, Text value,
>>>  OutputCollector<Text, MyWritable> output, Reporter reporter)
>>> throws IOException {
>>> String str = value.toString();
>>>  MyWritable text = new MyWritable("line " + line + " : " + str);
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Mohammad Tariq 2013-07-25, 19:27