Thanks, for your response. Just to make my question clear i want to have
hashMap and declare it as follows
public static class MapClass extends MapReduceBase implements Mapper {
private final static LongWritable ONE = new LongWritable(1);
private static Map usersMap=null;
public static Map getUsersMap(){
if(usersMap==null){
usersMap=new HashMap();
}
return usersMap;
}
........
public void map(WritableComparable key, Writable value,
OutputCollector output, Reporter reporter)
throws IOException {
.......
// nkey is object
//name is Text
if(getUsersMap().get(nKey)==null){
output.collect(name, ONE);
getUsersMap().put(nKey,
data[12]);
}
......
}
the problem is my hashmap(userMap) is always empty.Now I hope
my problem is clear.
Thanks,
Helen
Ted Dunning-3 wrote:
>
>
> This sounds like there is a little bit of confusion going on here.
>
> It is common for people who are starting with Hadoop that they are
> surprised
> when static fields of the mapper do not get shared across all parallel
> instances of the map function. This is, of course, because you are
> running
> many mappers.
>
> Usually when people say what you are saying, the reason is that they are
> trying to do something like removing duplicate elements. The best way to
> do
> that is to NOT try to put state into the map function, but rather to use
> the
> reduce and sorting functions to do the work. A good example is trying to
> find all of the unique words in a set of documents. If you just use a
> word-counting function, you get what you want (a list of unique words).
> If
> you want a list of unique words per day, then you simply have to change
> the
> program so that the mapper outputs a key that contains the word and the
> day
> and do the count as before.
>
> Remember also that your program may contain several map/reduce steps.
>
> Perhaps if you say more about what you are trying to do, it would be
> easier
> to help you.
>
>
> On 12/28/07 6:35 AM, "helena21" <[EMAIL PROTECTED]> wrote:
>
>>
>> Hi Everybody,
>>
>> i want to create arraylist that collects some objects from the input in
>> the
>> mapper class so that i want to use these collections to filter my input.
>> the
>> problem is my arraylist can't have even one object in it. its size is
>> always
>> zero. pls pls point me how can i create arraylist or other collection
>> objects. i make it static object but still the arraylist can't collect
>> any
>> object.
>>
>> Thanks
>> Helen
>
>
>
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