timespacex '+:^:(2&|)"0 i.100000' 0.0292787 2.10074e6 timespacex ']`+:@.(2&|)"0 i.100000' 0.00561727 7.08134e6 above code doubles odd numbers, and returns even numbers unchanged. I've previously noticed that ^: seemd faster than ]`u at . ... but I guess not?