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https://issues.apache.org/jira/browse/SPARK-12623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15082739#comment-15082739
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Sean Owen commented on SPARK-12623:
-----------------------------------
There is a {{preservesPartitioning}} flag on some API methods that lets you
specify that your function of {{(key, value)}} pairs won't change keys, or at
least won't change the partitioning. Unfortunately, for historical reasons this
wasn't exposed on the {{map()}} function, but was exposed on {{mapPartitions}}.
It's a little clunky to invoke if you only need map, but not much -- you get an
iterator that you then map as before.
That would at least let you do what you're trying to do. As to exposing a
specialized method for this, yeah it's not crazy or anything but I doubt it
would be viewed as worth it when there's a fairly direct way to do what you
want. (Or else, I'd say argue for a new param to map, but that has its own
obscure issues.)
> map key_values to values
> ------------------------
>
> Key: SPARK-12623
> URL: https://issues.apache.org/jira/browse/SPARK-12623
> Project: Spark
> Issue Type: New Feature
> Components: Spark Core
> Reporter: Elazar Gershuni
> Priority: Minor
> Labels: easyfix, features, performance
> Original Estimate: 0.5h
> Remaining Estimate: 0.5h
>
> Why doesn't the argument to mapValues() take a key as an agument?
> Alternatively, can we have a "mapKeyValuesToValues" that does?
> Use case: I want to write a simpler analyzer that takes the argument to
> map(), and analyze it to see whether it (trivially) doesn't change the key,
> e.g.
> g = lambda kv: (kv[0], f(kv[0], kv[1]))
> rdd.map(g)
> Problem is, if I find that it is the case, I can't call mapValues() with that
> function, as in `rdd.mapValues(lambda kv: g(kv)[1])`, since mapValues
> receives only `v` as an argument.
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