spark - filter withing map

I am trying to filter inside map function. Basically the way I'll do that in classic map-reduce is mapper wont write anything to context when filter criteria meet. How can I achieve similar with spark? I can't seem to return null from map function as it fails in shuffle step. I can either use filter function but it seems unnecessary iteration of data set while I can perform same task during map. I can also try to output null with dummy key but thats a bad workaround.