Github user mengxr commented on the pull request:
https://github.com/apache/spark/pull/268#issuecomment-38988446
@yinxusen Thanks for working on this! I don't think row statistics are
important because they represent values for different features. For column
statistics, instead of implementing each statistic separately, we can compute
all common statistics like (n, nnz, mean, variance, max, min) in a single job.
This adds little overhead to the computation.
Btw, `Vector.toArray` is an expensive operation for `SparseVector`. You
should use breeze's axpy to aggregate vectors.
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