Using a String to select a structure in a .mat file

Hello,

I was given a .mat file that contains structures named:

c1_01, c1_02, c1_03,c1_04,..., c1_14

All these structures have some data inside that I need extracted individually and add a new field to that stucture that is:

c1_01.r = (some variable in my script)

where the variable is calculated in the script. I need to do this for all the data and at the end, save the entire .mat file so that the new field is saved.

The issue I am running into is actually the iteration through these structures. I have tried using

i = 1:14
if(i<10);
name = sprintf('c1_0%d',i);
end
if(i>=10)
name = sprintf('c1_%d',i);
end
fx = name.force; %force is the name of a field in the structure. 

Is there anyway to iterate through structures in this manner? How can I go about solving this?

[Adam Danz]

Did you create the mat file that stores those c1_## vlaues? Numbered variables are often a sign of inefficient data organization. See this link for an explanation.

A better approach would be to create a structure array and the problem you're describing would be very easy to solve with structure arrays.

[Mauricio Gomez]

Hi thank you for your input! Sadly, I did not create the mat file myself, another coworker did and I am unsure as to where he obtained the data from.

[Adam Danz]

Hmmm....

Off the top of my head, maybe you can load the variables in as a structure using S = load(___). Assuming all of the loaded variables are c1_01, c1_02, c1_03, etc, they would be fields of S and you could merely loop through the fields using

fn = fieldnames(S); 
for i = 1:numel(fn)
   C = S(fn{i});  % the i-th field in S
end

*fixed typos (blush)

[J. Alex Lee]

I'm sure you'll figure out the minor typos, but I think rather:

S = load("filename.mat");
fn = fieldnames(S); 
for i = 1:numel(fn)
   C = S.(fn{i});  % the i-th field in S
end

If you need access to the value of "i" for your script to generate the right data for the .r field you wish to append, you could also do (and using Adam's suggestion of structure array for easier future processing)

S = load("filename.mat");
for i = 14:-1:1
    C(i) = S.(sprintf('c1_%01d',i)))
    C(i).r = mynewdata;
end
save("newfile.mat","C")

If you have to stick with the current scheme then I think this would work

S = load("filename.mat");
for i = 1:14
    C = S.(sprintf('c1_%01d',i)))
    
    C.r = mynewdata;
    
    S.(sprintf('c1_%01d',i))) = C;
end

save("newfilename.mat","-struct","S")