PillarsListToArr: Make a list of pillars back into a 3D array.
Description
#' Suppose the array is of dimension n1 * n2 * n3, then pillar
[i, j, ] is list element i + n1 * (j - 1), so the first element
is pillar [1, 1, ], the second is pillar [1, 2, ] and so on.