Indexing a matrix with an array

Let's say I have a 4x4 matrix A. I can then get the item in place [2,3] by typing A(2,3).

Now let's say I have an array I=[2,3]. I would like to be able to write something like A(I) to get the same result as above. How could I do that?

Thanks.

Answer 1

[Stephen23]

Use a cell array, e.g.:

C = {2,3}; % use NUM2CELL(I) if required.
A(C{:})

Tested:

>> A = rand(4,4)
A =
   0.340974   0.252464   0.596849   0.800738
   0.064510   0.270160   0.242550   0.518083
   0.546270   0.318667   0.581832   0.409444
   0.814609   0.675596   0.588558   0.353607
>> C = {2,3};
>> A(C{:})
ans =  0.24255

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

[John Jönsson]

Thank you very much. Is there a function similar to zeros(1,n) or ones(1,n) where I can make C = {0,0,0,0,0,...} of length n? And what is C called? Do we call it a set?

[Stephen23]

"Is there a function similar to zeros(1,n) or ones(1,n) where I can make C = {0,0,0,0,0,...} of length n?"

Here are two ways:

C = repmat({0},1,n)
C = num2cell(zeros(1,n))

"And what is C called?"

a cell array:

https://www.mathworks.com/help/matlab/cell-arrays.html

MATLAB does not have a "set" data type:

https://www.mathworks.com/help/matlab/matlab_prog/fundamental-matlab-classes.html