Indexing of cell array and a vector

Hi guys, my problem has been raised before but with some differences.

I have a cell array of indexes, index. Its cells can be zero or vectors with several values. On the other hand I have a data vector, data. I need a cell array, out, that relates data to indexes, preferably without using a loop.

For example:

index = {[0], [0], [5], [0], [6, 7], [0], [0], [1], [0], [0], [0], [ 3]} ;
data = [100, 10, 20, 15, 11, 25, 200, 45];

Desired result:

out = {[0], [0], [11], [0], [25, 200], [0], [0], [100], [0], [0], [20]}

Can somebody help me?

[Stephen23]

"preferably without using a loop."

Why?

[Sergio Rojas Blanco]

Hi Stephen23, my data cell is quite large and I think a loop would be slower, right?

[Stephen23]

"I think a loop would be slower, right?"

A well-written FOR-loop would likely be faster than code using CELLFUN, ARRAYFUN, or anything else.

Who taught you the oddly-persistent myth that FOR-loops are slow?

[Sergio Rojas Blanco]

Actually, I don't know the internal process of cellfun or arrayfun. Possibly, they perform a loop and, therefore, it would be difficult to choose the most efficient procedure, but I don't know, and I have assumed that loops take longer. It would have to be checked experimentally.

In any case, I thank you very much for your contributions. They have helped me a lot

Answer 1

[Star Strider]

One approach —

index = {[0], [0], [5], [0], [6, 7], [0], [0], [1], [0], [0], [0], [ 3]} ;
data = [100, 10, 20, 15, 11, 25, 200, 45];

q = cellfun(@(x) data(x(x>0)), index, 'Unif',0);
Lvc = cellfun(@(x) all(x==0), index, 'Unif',0);                     % Using 'all' Is Necessary To Make The Logical Indices Work Correctly

out = index;
out(~[Lvc{:}]) = q(~[Lvc{:}])

out = 1x12 cell array
    {[0]}    {[0]}    {[11]}    {[0]}    {[25 200]}    {[0]}    {[0]}    {[100]}    {[0]}    {[0]}    {[0]}    {[20]}

.

[Sergio Rojas Blanco]

It works! Thank you very much :D

[Star Strider]

As always, my pleasure!