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From "Hui Wen Han (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-2007) Is it possible that use ArrayList or other type instead Iterable when use reduce(Object, Iterable, Context)?
Date Thu, 12 Aug 2010 15:57:17 GMT
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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