Github user mengxr commented on the pull request:
https://github.com/apache/spark/pull/304#issuecomment-40024806
@sryza I made one pass over the code. Besides the inline comments:
1. The output of one-hot is always sparse, we should use sparse vector
instead of dense.
2. This is part of feature transformation. Using `Array` to store features
would result reallocation of memory. We should spend more time on the data
types.
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