[jira] Created: (MAPREDUCE-2007) Is it possible that use ArrayList or other type instead Iterable when use reduce(Object, Iterable, Context)?

[Hui Wen Han (JIRA)]

Is it possible that use ArrayList or other type  instead Iterable  when use 
reduce(Object, Iterable, Context)?
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                 Key: MAPREDUCE-2007
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2007
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
    Affects Versions: 0.20.2
            Reporter: Hui Wen Han
             Fix For: 0.20.2


1) Sometimes We only need get the elements count of the input values of Reducer 
task,

but we have to iterate all the input values to calculate it.

2) Sometimes We only need get a few elements (for example top n,last n ,or 
random ) from  the input values of Reducer task,

if it can use ArrayList or other type  instead Iterable  when use 
reduce(Object, Iterable, Context),it 's more conveniency.

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