GitHub user mpjlu opened a pull request:

    [SPARK-21680][ML][MLLIB]optimzie Vector coompress

    ## What changes were proposed in this pull request?
    When use Vector.compressed to change a Vector to SparseVector, the 
performance is very low comparing with Vector.toSparse.
    This is because you have to scan the value three times using 
Vector.compressed, but you just need two times when use Vector.toSparse.
    When the length of the vector is large, there is significant performance 
difference between this two method.
    ## How was this patch tested?
    The existing UT

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

    $ git pull optVectorCompress

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

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

    This closes #18899
commit 5dc5c89242a0c2a5ac6a693c3703eef8ee160616
Author: Peng Meng <>
Date:   2017-08-10T01:59:17Z

    optimzie Vector coompress


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