Index Item?

Hey all!,
Quick, super simple question. Looked around for the answer but must not have been phrasing the question right, but here goes.

How can i extract out a number from each index. The screen shot shows a list of x,y,z coordinates of a field of points. I want alllll the x's in a new list. so if i have
0:252,254,129
1:229,245,137
2-x:etc,etc,etc

I want a new list with
0:252
1:229
2-x:etc
thanks guys!