Hello. If I get you right I think you can use WHERE in your case. Given P arrays of size MxN. Then the following code will give you array of max values and array of numbers of array with max value for each element. arr = fltarr(M, N, P) ; given arrays maxarr = fltarr(M, N) ; here we put maximum values Imaxidx = intarr(M, N) ; here for each element we put number of array where this element is greatest among all other arrays maxarr[*, *] = -999999 ; or something really impossible for i = 0, P-1 do begin curarr = arr[*, *, i] ; let's take the i-th array idx = where ( curarr gt maxarr) ; find indices of elements of current array which are greater than such elements of maxarr if (idx[0] ne -1) then begin ; if there are any... maxarr[idx] = curarr[idx] ; ... we store maximum values for future comparison... maxidx[idx] = i ; ... and ordinal number (i) of current array for each maximum element endif endfor Should work. :) Bye!