[GitHub] incubator-beam pull request #741: Top improvements

[robertwb]

Github user robertwb closed the pull request at:

https://github.com/apache/incubator-beam/pull/741


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[GitHub] incubator-beam pull request #741: Top improvements

[robertwb]

GitHub user robertwb opened a pull request:

https://github.com/apache/incubator-beam/pull/741

Top improvements

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You can merge this pull request into a Git repository by running:

$ git pull https://github.com/robertwb/incubator-beam top

Alternatively you can review and apply these changes as the patch at:

https://github.com/apache/incubator-beam/pull/741.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

This closes #741


commit 9151fcf861704c550c21f411a9047f955f179ec4
Author: Robert Bradshaw 
Date:   2016-07-27T17:09:49Z

Better top implementation.

When selecting the top k of n, it is common that k << n.
Using a heap is O(n log k) while select algorithms can
achieve O(n + k log k).

This also avoids the ugliness that heapq does not take the
comparator as an argument, resulting in _HeapItem classes that
were cumbersome and expensive to serialize.

commit e38d6f60f18bf6ad61f2d387c67efa2012af2e14
Author: Robert Bradshaw 
Date:   2016-07-27T19:23:02Z

Allow Top operations to take key argument rather than compare, and order
by the natural ordering if neither is specified.




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