
Trying to use ReplacePart
Posted:
Jun 30, 2011 8:00 PM


Hi!
I needed some days ago to replace elements in a matrix. My first thought was to use ReplacePart, but I found myself trying to tell it to make all replacements at once, instead of returning multiple copies of the original matrix with only one element changed. As I was in a hurry, I solved the problem in a different way. However I'm still wondering how can I use a more "natural" code to solve this problem.
nNum = 3; nQnum = 2;
cNum = 2^(nNum  nQnum); cQnum = 2^(nNum  1);
list = Table[i, {i, 1, cQnum}]; list1 = Partition[list, cNum]; matrix = ConstantArray[0, {cQnum, cQnum}]; matrix1 = RandomInteger[{1, 10}, {2^nNum, 2^nNum}]
(matrix[[#[[1]], #[[2]]]] = matrix1[[ cNum*Position[list1, #[[1]]][[1, 1]] + #[[1]], cNum*Position[list1, #[[2]]][[1, 1]] + #[[2]]]]) & /@ Tuples[{list, list}];
or a faster solution,
Table[matrix[[i, j]] = matrix1[[ cNum*Position[list1, i][[1, 1]] + i, cNum*Position[list1, j][[1, 1]] + j]], {i, 1, cQnum}, {j, 1,cQnum}];

