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<CENTER><A HREF = "http://mapreduce.sandia.gov">MapReduce-MPI WWW Site</A> - <A HREF = "Manual.html">MapReduce-MPI Documentation</A>
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<H3>MapReduce clone() method
</H3>
<PRE>uint64_t MapReduce::clone()
</PRE>
<P>This calls the clone() method of a MapReduce object, which converts a
KeyValue object directly into a KeyMultiValue object. It simply turns
each key in KeyValue object into a key in the new KeyMultiValue
object, with the same value. The method returns the total number of
key/value pairs in the KeyMultiValue object, which will be the same as
the number in the KeyValue object.
</P>
<P>This method essentially enables a KeyValue object to be passed
directly to a reduce operation, which requires a KeyMultiValue object
as input. Typically you would only do this if the keys in the
KeyValue object are already unique, to avoid the extra overhead of an
<A HREF = "aggregate.html">aggregate()</A> or <A HREF = "convert.html">convert()</A> or
<A HREF = "collate.html">collate()</A>, but this is not required. If they are not,
then there will also be duplicate keys in the KeyMultiValue object.
</P>
<P>Note that one of the <A HREF = "map.html">map()</A> methods allows an existing
KeyValue object to be passed as input to a user mymap() function,
generating a new Keyvalue object in the process. Thus there is
typically no need to invoke clone() followed by
<A HREF = "reduce.html">reduce()</A>.
</P>
<P>This method is an on-processor operation, requiring no communication.
When run in parallel, the key/value pairs of the new KeyMultiValue
object are stored on the same processor which owns the corresponding
KeyValue pairs.
</P>
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<P><B>Related methods</B>: <A HREF = "collapse.html">collapse()</A>, <A HREF = "collate.html">collate</A>,
<A HREF = "convert.html">convert()</A>
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