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Date: Thu, 15 Sep 2011 00:16:27 -0500
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 <CAD+YOd-pSHPzQ5_Wr-PpPr+a6xeiq6XhZzuty27-8iO8h2B08A@mail.gmail.com>
Subject: Re: Reducers without output files
From: Arko Provo Mukherjee <arkoprovomukherjee@gmail.com>
To: mapreduce-user@hadoop.apache.org
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Hello,

Many thanks for your reply!

So to clarify, I should do the following:
public static class Reduce extends MapReduceBase implements
Reducer<IntWritable, Text, NullWritable, Text> {

reduce ()  {  // Pseudo reduce funtion - ignoring the proper syntax

// The processing goes here.
output.collect ( new NullWritable(), new Text(output_string) );


}

}

Finally in the main method of the Driver Class:

// For the Map Class
jobconf.setMapOutputKeyClass(IntWritable.class);
jobconf.setMapOutputValueClass(Text.class);

// For the Reduce Class
jobconf.setOutputKeyClass(NullWritable.class);
jobconf.setOutputValueClass(Text.class);

Please do correct me if my understanding is wrong.

Thanks again for your help!

Warm Regards
Arko

On Wed, Sep 14, 2011 at 11:12 PM,  <bejoy.hadoop@gmail.com> wrote:
> Akro
> =A0 =A0 To add on, if you want to ignore =A0the key part then substitute =
key with NullWritable. And do the desired modification in driver class in p=
lace of output key type.
>
> Hope it helps
> Regards
> Bejoy K S
>
> -----Original Message-----
> From: bejoy.hadoop@gmail.com
> Date: Thu, 15 Sep 2011 04:09:12
> To: <mapreduce-user@hadoop.apache.org>
> Reply-To: bejoy.hadoop@gmail.com
> Subject: Re: Reducers without output files
>
> Hi Akro
> =A0 =A0 =A0 You can achieve the same within the existing mapreduce frame =
work itself. Give a NullWritable in place of reducer output value in reduce=
 function. In your driver class as well mention the output value type as Nu=
llWritable.
>
> ------Original Message------
> From: Arko Provo Mukherjee
> To: mapreduce-user@hadoop.apache.org
> ReplyTo: mapreduce-user@hadoop.apache.org
> Subject: Reducers without output files
> Sent: Sep 15, 2011 08:56
>
> Hello Everyone,
>
> I have a small issue with my Reducer that I am trying to figure out
> and wanted some advice.
>
> In the reducer, when writing to the output file as declared in
> FileOutputFormat.setOutputPath() I want to write only the key and not
> the value when I am calling output.collect().
>
> Is there a way I can ignore the key part?
>
> Else,
>
> Can I write a Reducer function that doesn't do a output.collect()??
>
> Say I omit the FileOutputFormat.setOutputPath() in the Driver Class.
>
> I can then manually write the output to HDFS in the format I like.
>
> Is this legal way to do stuff?
>
> Many thanks in advance!
> Warm Regards
> Arko
>
>
> Regards
> Bejoy K S