How can I create a variable for subscripts of an array?

Hello all,

I want to create and use a single variable for subscript range of a multi-dimensional array. I know for a 1D-array I can do:

array=ones(20,1);
indices=5:10;
array(indices)=0;

I tried something like this for a 3D-array, but it didnt work:

array=ones(10,10,10);
indices=[2:5,3:6,4:7];
array(indices)=0;

but it didnt work. Is it possible to create a variable that I can use in such manner? Thank you.

Answer 1

[Guillaume]

You need to convert your subscript indices into linear indices. You do that with sub2ind:

array(sub2ind(size(array), indices)) = 0;

edit: completely misread the question. The above is completely wrong. See discussion in the comments. The correct answer should have been:

indices = {2:5, 3:6, 4:7};
array(indices{:}) = 0;

[Renat]

It doesnt work. Whatever I do, whether I separate ranges with a comma or a semi-colon, it seems to treat each element of indices as a linear index. I seem to have found the solution though:

array=ones(10,10,10);
tmp=zeros(size(array));
tmp(2:5,3:6,4:7)=1;
indices=find(tmp);
array(indices)=0;

This may look silly, by what I needed was a variable, indices, which I can get from a function for example and then use it as a range for an array, and this seems to get the job done.

[Guillaume]

"It doesnt work"

Then don't accept the answer!

Of course, it doesn't work. I completely misread the question.

The main problem with your question is that it is flawed. You try to define indices as:

indices=[2:5,3:6,4:7]

The problem is that the above array is exactly the same as:

indices = [2:4, 5:-2:3, 4, 5:6, 4:7]

or

indices = [2, 3, 4, 5, 3, 4, 5, 6, 4, 5, 6, 7]

i.e. your distinction between the three ranges doesn't really exist. It's all concatenated into one vector

Now, to answer your question properly:

You need to define your dimension indices as a cell array

array = reshape(1:1000, 10, 10, 10);
indices = {2:5, 3:6, 4:7}  %notice how it's all three separate vectors

Using indices is then easy:

array(indices{:}) = 0

[Renat]

Well, I could unaccept, but your answer pushed me in the right direction of using linear indices and it worked in the end.

I didn't imply that my original way of assigning indices was correct. That was what first came to mind. I was looking for proper syntax of doing it. Thank you. This is a more efficient way of doing it.