Question

I have a simple problem with structures.

Lets create:

x(1).a(:, :) = magic(2);
x(2).a(:, :) = magic(2)*2;
x(3).a(:, :) = magic(2)*3;

how to list a(1, 1) from all x-es?

i wanted to do it like:

x(1, :).a(1,1)

but there is an error “Scalar index required for this type of multi-level indexing.”

How to approach it? I know I can do it with a loop, but that’s probably the worst solution 🙂
Thanks!

Answer 1

This is not the best datastructure to use if this is the sort of query you’d like to make on it, precisely because this sort of indexing cannot be done directly.

However, here is one approach that works:

cellfun(@(X) X(1,1), {x.a})

The syntax {x.a} converts x from a ‘struct array’ into a cell array. Then we use cellfun to apply a function as a map over the cell array. The anonymous function @(X) X(1,1) takes one argument X and returns X(1,1).