Hbase Map/reduce-How to access individual columns of the table?

[Ram <ru...@gmail.com>]

 have a table called User with two columns ,one called visitorId and the other 
called friend which is a list of strings. I want to check whether the VisitorId 
is in the friendlist. Can anyone direct me as to how to access the table columns 
in a map function? I'm not able to picture how data is output from a map 
function in hbase. My code is as follows.

ublic class MapReduce {

static class Mapper1 extends TableMapper<ImmutableBytesWritable, Text> {

    private int numRecords = 0;
    private static final IntWritable one = new IntWritable(1);


    private final IntWritable ONE = new IntWritable(1);
    private Text text = new Text();
    @Override
    public void map(ImmutableBytesWritable row, Result values, Context context) 
throws IOException {

        //What should i do here??how do i access the individual columns and       
compare?
        ImmutableBytesWritable userKey = new ImmutableBytesWritable(row.get(), 
0, Bytes.SIZEOF_INT);

       context.write(userkey,One);  
                 }

            //context.write(text, ONE);
        } catch (InterruptedException e) {
            throw new IOException(e);
        }

    }
}



public static void main(String[] args) throws Exception {
    Configuration conf = HBaseConfiguration.create();
    Job job = new Job(conf, "CheckVisitor");
    job.setJarByClass(MapReduce.class);
    Scan scan = new Scan();
    Filter f = new RowFilter(CompareOp.EQUAL,new SubstringComparator("mId2"));
    scan.setFilter(f);
    scan.addFamily(Bytes.toBytes("visitor"));
    scan.addFamily(Bytes.toBytes("friend"));
    TableMapReduceUtil.initTableMapperJob("User", scan, Mapper1.class, 
ImmutableBytesWritable.class,Text.class, job);

}

Re: Hbase Map/reduce-How to access individual columns of the table?

[Doug Meil <do...@explorysmedical.com>]

Hi there-

Have you seen the chapter on MR in the RefGuide?

http://hbase.apache.org/book.html#mapreduce.example

You use the Result instance just like you would from a client program.




On 4/17/12 6:07 AM, "Ram" <ru...@gmail.com> wrote:

> have a table called User with two columns ,one called visitorId and the
>other 
>called friend which is a list of strings. I want to check whether the
>VisitorId 
>is in the friendlist. Can anyone direct me as to how to access the table
>columns 
>in a map function? I'm not able to picture how data is output from a map
>function in hbase. My code is as follows.
>
>ublic class MapReduce {
>
>static class Mapper1 extends TableMapper<ImmutableBytesWritable, Text> {
>
>    private int numRecords = 0;
>    private static final IntWritable one = new IntWritable(1);
>
>
>    private final IntWritable ONE = new IntWritable(1);
>    private Text text = new Text();
>    @Override
>    public void map(ImmutableBytesWritable row, Result values, Context
>context) 
>throws IOException {
>
>        //What should i do here??how do i access the individual columns
>and       
>compare?
>        ImmutableBytesWritable userKey = new
>ImmutableBytesWritable(row.get(),
>0, Bytes.SIZEOF_INT);
>
>       context.write(userkey,One);
>                 }
>
>            //context.write(text, ONE);
>        } catch (InterruptedException e) {
>            throw new IOException(e);
>        }
>
>    }
>}
>
>
>
>public static void main(String[] args) throws Exception {
>    Configuration conf = HBaseConfiguration.create();
>    Job job = new Job(conf, "CheckVisitor");
>    job.setJarByClass(MapReduce.class);
>    Scan scan = new Scan();
>    Filter f = new RowFilter(CompareOp.EQUAL,new
>SubstringComparator("mId2"));
>    scan.setFilter(f);
>    scan.addFamily(Bytes.toBytes("visitor"));
>    scan.addFamily(Bytes.toBytes("friend"));
>    TableMapReduceUtil.initTableMapperJob("User", scan, Mapper1.class,
>ImmutableBytesWritable.class,Text.class, job);
>
>}
>
>