Question

I have a matrix of structs:

s(1:2,1:3) = struct('a',1,'b',2);

I have a function that has 2 int inputs, and calculates an int values according
to some logic. How can I Apply the function on all the matrix s using the fields of each struct (‘a’ and ‘b’) as input for the function. The result matrix should be the same size as s just with the result of the function as data.

function f = SomeFunctionIWrote(a,b)
    %...Some calculations...
    f = result;
 end

Thanks,
Guy.

Answer 1

Applying the same function to each element of an array is what arrayfun is built for (see this blog post by Loren Shure for a helpful discussion/example).

If f is your function and s is an array of structures with fields a and b,

result = arrayfun(@(x)f(x.a,x.b), s);

will do the trick. @(x) is an anonymous function if you haven’t come across those before.

If the function doesn’t return a scalar, use the 'uniformoutput' option (set to false) so that result becomes a cell array.

result = arrayfun(@(x)f(x.a,x.b), s, 'uniformoutput', false); 

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Note 1: arrayfun is slow! Often (always?) slower than a loop. The advantage of it (in my experience/opinion) comes from not having to deal with size/shape of matrix dimensions if/when your code changes, and shorter code that is easier to read.

Note 2: you can use 'uni' and 0 in place of 'uniformoutput' and false to save typing/line space, though at the expense of clarity