Question

I am hoping to have a multidimensional array of structures, but I can’t seem to get at the field of the contained elements. or in code:

mySample = struct('a', zeros(numA),'b', zeros(numB));
Data = cells(height,width);
disp(Data(1,1).a);

The bottom line fails with an error such as

“Improper index matrix reference.”

How is a 2D array of structures done in Matlab?

Answer 1

There are a couple of ways to create an array of structures (“structure array” or “struct array”). Note that in a struct array, each element must have the same fields. For example, if s(1) has fields “a” and “b”, then s(2)..s(n) must have fields “a” and “b”.

% num rows
n = 10;
% num cols
m = 50;

% method 1, which will repeat a structure
s = struct('field1', 10, 'field2', 20);
sArray = repmat(s, n, m);

% method 2, which initializes each field to empty []
sArray(n,m) = struct('field1', [], 'field2', []);

You can expand on that to go beyond the second dimension eaisly:

sArray(n,m,p) = struct('field1', [], 'field2', []);

You could also preallocate the array and use a for-loop to set the value of each field. Additionally:

help deal
help structfun

You could also create a cell array of structures, which provides more flexibility: each structure in the cell array may have different fields.

c = cell(1,2);
c{1} = struct('a', 1, 'b', 2);
c{2} = struct('z', 0, 'q', 5);