about the down sample.

[zhangyuepeng]

thank you for the solution!
I have a problem about the negative down sampling.
you said :"to speed up training time, I down sample non-­events at 50:1 ratio." @owenzhang
because the evaluation is logloss, not the F1 or AUC. I think the negative down sampling can make the ratio of positive and negative become very different between train and test，this can make the logloss in test become larger.