Looping within a structure

Hello everyone,

Sorry if this question was already asked, but I couldnt find something that worked for me. I have the following Matlab struct

mystruct
    point1 : struct
    point2 : struct
    .
    .
    .
    .
    pointN : struct

Basically a structure containing point coordinates,

what I wish to do is basically fetch the data of the structure in a loop. Unfortunately I wasnt able to achieve this. What I created was

for i = 1:N

varName = strcat('mystruct.point',int2str(i));

%fetch data using the varname

end

Basically this is a snippet out of a bigger codeflow which I have simplified for the sake of my question.

Regards,

Sanjay

Answer 1

[Stephen23]

You can easily loop over the fieldnames:

F = fieldnames(mystruct);
for k = 1:numel(F)
    A = mystruct.(F{k});
    ... do whatever with A
end

or use numbers to generate the fieldnames:

for k = 1:N
    F = sprintf('point%d',k);
    A = mystruct.(F);
    ... do whatever with A
end

https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html

Note that your code would be simpler and more efficient if you used a non-scalar structure (or even a cell array), rather than accessing lots of fieldnames dynamically:

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

[Sanjay Kamath Madhengal]

Thanks, this really worked well for me. Accepting this as the answer :)

Answer 2

[Neuropragmatist]

What are the values stored in point1.struct?

Is your question about accessing fields of the table generally? If so you should look here:

https://uk.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

If you are asking how to extract all of the data into one matrix you might be able to use struct2table without needing your loop at all:

https://uk.mathworks.com/help/matlab/ref/struct2table.html

Then it's pretty easy to extract whole columns of data.

M.