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MapReduce, mail # user - Reading fields from a Text line

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Re: Reading fields from a Text line
Mohammad Tariq 2012-08-02, 12:39
Thank you everyone. Here is the code from the driver :

Configuration conf = new Configuration();
Job job = new Job(conf, "XPTReader");
Path inPath = new Path("/mapin/TX.xpt");
FileInputFormat.addInputPath(job, inPath);
FileOutputFormat.setOutputPath(job, new
System.exit(job.waitForCompletion(true) ? 0 : 1);

Bejoy : I have observed one strange thing. When I am using
IntWritable, the output file contains the entire content of the input
file, but if I am using LongWritable, the output file is empty.

Sri, Code is working outside MR.

    Mohammad Tariq
On Thu, Aug 2, 2012 at 4:38 PM, Bejoy KS <[EMAIL PROTECTED]> wrote:
> Hi Tariq
> I assume the mapper being used is IdentityMapper instead of XPTMapper class. Can you share your main class?
> If you are using TextInputFormat an reading from a file in hdfs, it should have LongWritable Keys as input and your code has IntWritable as the input key type. Have a check on that as well.
> Regards
> Bejoy KS
> Sent from handheld, please excuse typos.
> -----Original Message-----
> From: Mohammad Tariq <[EMAIL PROTECTED]>
> Date: Thu, 2 Aug 2012 15:48:42
> Subject: Re: Reading fields from a Text line
> Thanks for the response Harsh n Sri. Actually, I was trying to prepare
> a template for my application using which I was trying to read one
> line at a time, extract the first field from it and emit that
> extracted value from the mapper. I have these few lines of code for
> that :
> public static class XPTMapper extends Mapper<IntWritable, Text,
> LongWritable, Text>{
>                 public void map(LongWritable key, Text value, Context context)
> throws IOException, InterruptedException{
>                         Text word = new Text();
>                         String line = value.toString();
>                         if (!line.startsWith("TT")){
>                                 context.setStatus("INVALID LINE..SKIPPING........");
>                         }else{
>                                 String stdid = line.substring(0, 7);
>                                 word.set(stdid);
>                                 context.write(key, word);
>                         }
>                 }
> But the output file contains all the rows of the input file including
> the lines which I was expecting to get skipped. Also, I was expecting
> only the fields I am emitting but the file contains entire lines.
> Could you guys please point out the the mistake I might have made.
> (Pardon my ignorance, as I am not very good at MapReduce).Many thanks.
> Regards,
>     Mohammad Tariq
> On Thu, Aug 2, 2012 at 10:58 AM, Sriram Ramachandrasekaran
> <[EMAIL PROTECTED]> wrote:
>> Wouldn't it be better if you could skip those unwanted lines
>> upfront(preprocess) and have a file which is ready to be processed by the MR
>> system? In any case, more details are needed.
>> On Thu, Aug 2, 2012 at 8:23 AM, Harsh J <[EMAIL PROTECTED]> wrote:
>>> Mohammad,
>>> > But it seems I am not doing  things in correct way. Need some guidance.
>>> What do you mean by the above? What is your written code exactly
>>> expected to do and what is it not doing? Perhaps since you ask for a
>>> code question here, can you share it with us (pastebin or gists,
>>> etc.)?
>>> For skipping 8 lines, if you are using splits, you need to detect
>>> within the mapper or your record reader if the map task filesplit has
>>> an offset of 0 and skip 8 line reads if so (Cause its the first split