MATLAB: Accessing the nth dimension in a variable sized multidimensional array

multidimensional array

I have a large array of values, and before the execution I don't know how many dimension I need.
How can I extract a single column from this? Or even a specific value?
I tried things like writing a vector of the indices, but that didn't return a single value.
Example: I have a matrix A, how do I get A(1,1,…,1,:) when I don't know how many dimensions A has?
And what if I want to set a single dimension to a specific value like A(1,:,:,…,:)
Alternatively: is there another good way of storing high-dimensional scalar fields? I tried a list of index vectors like in a sparse matrix, but finding a specific value becomes very inefficient that way right?

Best Answer

"...how do I get A(1,1,...,1,:) when I don't know how many dimensions A has?"
You use a comma-separated list, which you can easily generate from a cell array:
C = {1,1,1,...1,,':'};
A(C{:})
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
You can create the cell array using repmat or num2cell or similar. The function ndims will also be useful here.
"...what if I want to set a single dimension to a specific value like A(1,:,:,...,:)"
Use a comma-separated list. Lets try a more practical example, where we define the size of C automatically:
C = repmat({':'},1,ndims(A));
C{1} = 1; % C{dim} = index
val = A(C{:})
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