importing selectivelyto Aperture from Iphoto

I am new to both Aperture and somewhat to iphoto. I have been unable to find a way to selectively import iphoto folders to aperture. How can I avoid getting doubles? Aperture does not seem to have a discretionary process, so when I imported from iphoto I ended up with a lot of doubles.
The "rolls" only show up in part. The rolls that I changed the name of do not show up when I try to import into aperture.
Can anyone help? I have tried the help sections on both programs and cannot find what I am looking for.
Thanks