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https://issues.apache.org/jira/browse/CRUNCH-57?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450003#comment-13450003
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Kiyan Ahmadizadeh commented on CRUNCH-57:
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On a similar note, is it expected that for a PCollection<T>, T is comparable?
Aggregate.max and Aggregate.min contain implementations that check that the
type class for the PCollection is Comparable. Given the MapReduce framework's
reliance on sorting, however, it seems like T should always be Comparable.
If it's not expected that T be Comparable, I would argue that max, min, and
sort functionality should be in a PCollection decorator that contains
operations for PCollections that contain comparable elements.
> Add a length function to PCollection
> ------------------------------------
>
> Key: CRUNCH-57
> URL: https://issues.apache.org/jira/browse/CRUNCH-57
> Project: Crunch
> Issue Type: New Feature
> Components: Core
> Affects Versions: 0.3.0
> Reporter: Kiyan Ahmadizadeh
> Assignee: Josh Wills
> Attachments: CRUNCH-57.patch
>
>
> Sometimes it's useful and interesting to compute the number of elements in a
> PCollection.
>
> For example, suppose there was an initial PCollection that was then filtered
> into another. If I'm interested in how many elements of the original
> PCollection matched the filter, I'll have to write extra code to compute this.
> PCollections should have a length method that, when called, computes the
> number of elements in the PCollection and returns the result.
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