Getting Data from a struct-array with other structs in it, without a loop

Hi Matlab Community,

I have got a problem getting data out of a struct-array (I think the structure is called struct-array) without using a for-loop.

I get data from simulations in the following structure:

Now I want to get a specific value (e.g. "PF") from all fields (1 to 12) in the struct PowerAnalysis.ECP.

The Power Analysis Struct has got this structure:

And the ECP Structure itself has got this structure:

I can access one result with the command:

K>> Post_Processing.RunData(1).PowerAnalysis.ECP.PF

ans =

    0.6738    0.6738    0.6738
    

But if I try to access all the field by this command:

  K>> Post_Processing.RunData(:).PowerAnalysis.ECP.PF
Expected one output from a curly brace or dot indexing expression, but there were 12 results.  

I tried various things to get whole data. Of course I could use a loop, but I think that there is an easier and faster way than using a loop.

I have tried someting with structfun, but that yields to the same problem as mentioned befor:

test = @(s) Post_Processing.RunData(s).PowerAnalysis.ECP.PF
K>> test(1)

ans =

    0.6738    0.6738    0.6738
    
    test(:)
Input arguments to function include colon operator. To input the colon character, use ':' instead.

It would be very helpful if someone can help me with the problem, because it bothers me for two days now.

A second questions is: How is my data structure called ? I would say it's a structure-array with sub structures in it. But if I google this structure I do not get helping results on my topic, so I think the structure isn't described right by me.

Thanks in advance and kind greetings,

M.G.

[Stephen Cobeldick]

"How is my data structure called"

Nested structures.

Answer 1

[Stephen Cobeldick]

Using arrayfun to iterate over the elements of non-scalar structure Post_Processing.RunData:

fun = @(s) s.PowerAnalysis.ECP.PF; % all sub-structures must be scalar!
out = arrayfun(fun, Post_Processing.RunData, 'uni',0);
mat = vertcat(out{:}) % optional

Note that arrayfun just hides the loop inside, and is generally slower than using an explicit loop.

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

Or concatenate scalar sub-structures using comma-separated lists:

tmp = [Post_Processing.RunData];
tmp = [tmp.PowerAnalysis];
tmp = [tmp.ECP];
out = {tmp.PF}; % or:
mat = vertcat(tmp.PF);

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

Why syntaxes like Post_Processing.RunData(:).PowerAnalysis.ECP.PF will not work:

https://www.mathworks.com/matlabcentral/answers/329538-why-do-i-get-this-error-for-this-non-scalar-structure