Nested Table With Iterable Bounds

Question

I have a set of data that looks vaguely like this:

data = {{{a,x1,y1,a},{a,x1,y1,a},{a,x1,y1,a},{a,x1,y1,a},{a,x1,y1,a}},
{{b,x2,y2,b},{b,x2,y2,b},{b,x2,y2,b}},
{{c,x3,y3,c},{c,x3,y3,c},{c,x3,y3,c},{c,x3,y3,c}}}

where the quantities I am interested in are the x and y values and the a, b, c are simply identifiers I don't need anymore.

I was attempting to extract those values and put them into a new set called positions that then looks like:

positions = {{{x1,y1},{x1,y1},{x1,y1},{x1,y1},{x1,y1}},
{{x2,y2},{x2,y2},{x2,y2}},
{{x3,y3},{x3,y3},{x3,y3},{x3,y3}}}

using a double table structure:

  positions = Table[{data[[1]][[i]][[2]], data[[1]][[i]][[3]]}, {j, 1, Length[data]}, {i, 1, Length[data[[j]]]}]

but it hasn't worked. I believe my problem is just where I have placed / how I have used the iterators. I was wondering if anyone could show me where I have gone wrong? Thanks!

Answer 1

You can write positions = data[[All, All, {2, 3}]], or by adjusting your code:

positions = Table[{data[[j]][[i]][[2]], data[[j]][[i]][[3]]},
              {j, 1, Length[data]}, {i, 1, Length[data[[j]]]}]

Answer 2

try Part:

data[[All, All, {2, 3}]]

{{{x1, y1}, {x1, y1}, {x1, y1}, {x1, y1}, {x1, y1}}, {{x2, y2}, {x2, y2}, {x2, y2}}, {{x3, y3}, {x3, y3}, {x3, y3}, {x3, y3}}}