MATLAB: Apply function to each column of matrix for all columns without for loop

computationfor loop

Hi all,

I have a function "Func(X)" which operations on n-by-1 single column matrix "X" and outputs a scalar quantity. I also have a n-by-m matrix "A" that I would like to apply "Func" for all m columns in "A" and obtain 1-by-m matrix, say B, as a result without using for loop or any iterative definitions. What is the best way to proceed with this?

Best Answer

There is no general way that is more efficient than a for-loop, but if you are just trying to hide the loop, then you can do things like this:

 B=cell2mat( arrayfun(@(i) Func(A(:,i)) , 1:size(A,2), 'uni',0) );

 B = splitapply(@Func,A,1:size(A,2));

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MATLAB: I have an all zero matrix ‘a’ of size m x n. In a new 2 column matrix ‘b’ I have the indices where I should replace the zero in ‘a’ with 1. Is there a way to do this without a ‘for’ loop? The m,n > 500..

sparse() is the easiest way to handle this. Another way is

A( sub2ind(size(A),B(:, 1),B(:, 2)) = 1;

MATLAB: Selecting different element of a matrix with each function operation

Hi JD,

You could pass a counter variable i to your function as such:

i = 1;
while condition
  i = i+1;
end
function y = func(x, i)
  global A;
  y = x - A(i,2);
end

Best Answer

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MATLAB: I have an all zero matrix ‘a’ of size m x n. In a new 2 column matrix ‘b’ I have the indices where I should replace the zero in ‘a’ with 1. Is there a way to do this without a ‘for’ loop? The m,n > 500..

MATLAB: Selecting different element of a matrix with each function operation

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