[Haskell-beginners] reorganizing lists

Hi All, At the moment I have a list of lists. The inner list is a coordinate, like (x,y) but is [x,y] instead. What I would like to do is group all the x's into one list, and the y's into another. I know I can do this with calling 2 maps on the container, but I would also like to do this in one iteration. Does anyone have any ideas? Thanks in advance, Bryce