Rebuild a list ?

Hi,

I am using image sampler to control the radius of 200 circles, my problem is that I am trying to change the values given by image sampler. Instead of almost 200 different values ranging from 0 to 1, I would like only 4 radius, 0, 0.25, 0.50, 1.

I don't know if I do it right, I am using dispatch to isolate them, but now I end up with 4 lists and I would like to know how I can use this 4 lists to select the values directly from my first list or rebuild the first list with my 4 sub lists ?

Thanks