MATLAB: Unknown number of output variables

comma-separated-listsMATLAB

There are some functions that support variable number of output variables. For example, ind2sub(), depending on the matrix size, could have variable number of output.
if I type:
[I1,I2]=ind2sub([3,4],10);
I get the correct answer, I1=1 and I2=4;
but if I issue:
subIndices=ind2sub([3,4],10);
then I won't get subIndices= [1,4]; but I get subIndices=10; which definitely is not what I wanted.
Now here is my quesitons. What if I don't know the input size and that is defined during the runtime, meaning that my input size once might be [3,4] and another time it would be [3,4,5]. So once I need to call [I1,I2]=ind2sub([3,4],10) but another time I need to have [I1,I2,I3]=ind2sub([3,4,5],10) in the code.
In this easy case I just rewrote another version of ind2sub which outputs the indices as vector, you can see the code at the end of this post; but what is a better way of doing this?
P.S. I don't want to construct the command string and use eval()
Here is the modified version of ind2sub():
function subIndices = myInd2Sub(inputSize,index)
%%myInd2Sub is similar to MATLAB's ind2sub except that the output, i.e. 
%  the indices for each dimensions, are provided in a single array, instead
%  of separate output variables.
      % Checking input arguments
      validateattributes(inputSize, ...
                         {'numeric'}, ...
                         {'vector','integer','positive'});
      validateattributes(index, ...
                         {'numeric'}, ...
                         {'scalar','integer','positive','<=',prod(inputSize)});
      % preparing the output
      subIndices = zeros(numel(inputSize),1);
      % changing the index to zero-base
      index = index - 1;
      % calculating the indices for each dimension
      for i=numel(subIndices):-1:2
          nElem = prod(inputSize(1:i-1));
          subIndices(i) = floor(index/nElem);
          index = index - subIndices(i)*nElem;
      end
      subIndices(1) = index;
      % changing back the indices to 1-base.
      subIndices = subIndices + 1;
  end

Best Answer

Use comma-separated lists (CSLs.)
 % User specifies number of inputs/outputs at runtime
 N = input('Enter number of dimensions to mesh (2-5) ');
 % Inputs to NDGRID specified at runtime by user as elements of a cell array
 inputs = repmat({[0,1]}, 1, N);
 % Outputs from NDGRID specified at runtime by user as elements of a cell array
 outputs = cell(1, N);
 % Call NDGRID with specified number of inputs and outputs by turning cell arrays into CSLs
 [outputs{:}] = ndgrid(inputs{:});
 % Use the outputs to display the coordinates of one of the points on the grid
 d = input(sprintf('Enter an integer value between 1 and %d ', 2^N));
 fprintf('Your combination is:')
 for k = 1:N
    fprintf(' %d', outputs{k}(d));
 end
 fprintf('\n')
I didn't add in any error checking for the values of N or d because this is a very quick example. But I wouldn't use too large an N as it could use a lot of memory.
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