How to access all elements within a structured cell array without looping?

I have a variable that look like this:

a_structure{1}.field1=vector1;

a_structure{2}.field1=vector2;

a_structure{3}.field1=vector3;

Without looping, how do I obtain the matrix that puts vector1 in column 1, vector2 in column 2 and vector3 in column 3?

Note: The {} in there is intentional. I am not using the structure(1).field1 syntax. I could get there, but would have thousands of lines of code to change.

Answer 1

[Cam Salzberger]

Hello Steve,

I would suggest restructuring your data storage. If you did use the struct array method of storage, I believe it would be as simple as [a_structure.field1]. But taking it as it is, you can fairly easily transform the cell array of similar structures into a struct array with this:

sArr = [a_structure{:}];

And then extract the fields into a matrix with my original method:

A = [sArr.field1];

The structures would need to be similar though. If the first line fails because they are not, you may need to use cellfun:

C = cellfun(@(c) c.field1, a_structure, 'UniformOutput', false);
A = [C{:}];

[SteveR]

WE HAVE A WINNER!!!! Thanks a ton, Cam! I knew there was something better than a loop out there (I was going down the subsref rabbit hole when I decided to post my first question here instead).

Rest assured, I will update my code to () syntax when I have enough spare time to ensure equivalent performance across the multitude of twists and turns my code takes. :)

Answer 2

[Stephen23]

"I am not using the structure(1).field1 syntax"

You should be. It would allow you to use efficient syntaxes for accessing your data (i.e. like you are asking about now):

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

If all of the structures in the cell array have the same fields and have compatible sizes, then you can concatenate them together, e.g. where C is your cell array:

S = [C{:}]; % concatenate unfortunate cell of structs into better non-scalar structure.
M = [S.field1] % concatenate field1 vectors [S(1).field1,S(2).field1,S(3).field1,...]

Read more:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

[SteveR]

I realized my error regarding the superiority of the () syntax some time ago, but project deadlines have kept me from fixing the thousands of lines of code I have across several different analysis tools.