tree 1db7cd65cfa869eb54d14e4f8f85f6e6e40d6fbc
parent 55395490e7a642c5001b26f55e18cafe7fefaeec
author Christopher Nguyen <ctn@adatao.com> 1370409167 -0700
committer Matei Zaharia <matei@eecs.berkeley.edu> 1371915612 -0700

In the current code, when both partitions happen to have zero-length, the return mean will be NaN.
Consequently, the result of mean after reducing over all partitions will also be NaN,
which is not correct if there are partitions with non-zero length. This patch fixes this issue.