Amit, it's not used here in this example, but it has other uses.
As I needed, you can pass in the name of input file as key, for example.
Rasit
2009/3/1 Kumar, Amit H. <ahku...@odu.edu>
> A very Basic Question:
>
> Form the WordCount example below: I don't see why do we need the
> "LongWritable key" argument in the Map function. Can anybody tell me the
> importance of it?
> As I understand the worker process reads in the designated input split as a
> series of strings. Which the map functions operates on to produce the <key,
> value> pair, in this case the 'output' variable. Then, Why would one need
> "LongWritable key" as the argument for map function?
>
> Thank you,
> Amit
>
> <snip>
> public static class MapClass extends MapReduceBase
> implements Mapper<LongWritable, Text, Text, IntWritable> {
>
> private final static IntWritable one = new IntWritable(1);
> private Text word = new Text();
>
> public void map(LongWritable key, Text value,
> OutputCollector<Text, IntWritable> output,
> Reporter reporter) throws IOException {
> String line = value.toString();
> StringTokenizer itr = new StringTokenizer(line);
> while (itr.hasMoreTokens()) {
> word.set(itr.nextToken());
> output.collect(word, one);
> }
> }
> }
> </snip>
>
>
>
--
M. Raşit ÖZDAŞ
