Sampling random negative based on sparse features
Sampling random negative based on sparse features

Summary: Avoid labelling objects similar to true positive (according to raw ID features) as negative.

Reviewed By: chocjy

Differential Revision: D5336506

fbshipit-source-id: 05f68f5d0af2a6eb907963d38702f0d6e9b2f99b

davinwang/caffe2,sf-wind/caffe2,xzturn/caffe2,Yangqing/caffe2,sf-wind/caffe2,xzturn/caffe2,Yangqing/caffe2,caffe2/caffe2,pietern/caffe2,davinwang/caffe2,pietern/caffe2,davinwang/caffe2,pietern/caffe2,xzturn/caffe2,sf-wind/caffe2,sf-wind/caffe2,Yangqing/caffe2,xzturn/caffe2,Yangqing/caffe2,davinwang/caffe2,Yangqing/caffe2,pietern/caffe2,davinwang/caffe2,pietern/caffe2,sf-wind/caffe2,xzturn/caffe2