MATLAB: Storing values in a structure

Good day MATLAB pros,

I have a long list of (single value) variables in my workspace that has to be stored into an array for every loop of execution.

Here's a simple example: Variables in the workspace:

a = 1;
b = 2.2;
c = 3.4;
d = [0.5 0.7 1 1.2 1.5];
e = [-15 -10 -5 0 5 10 15 20];
serial = {'WTZ00151'};
model = {'336F'};

NameList = {'a';'serial';'model'};

1) Here, I'm saving only the single value variables into Data structure, however what I'd like to do is for every loop, save the single values into an array in Data structure.

varList = who;
Data = struct;

fields = fieldnames(Data, '-full');
fieldSizes = structfun(@(field) length(field),Data);

% removing arrays from structure
for lst = 1:length(fieldSizes)
    if fieldSizes(lst) > 1
        Data = rmfield(Data,fields(lst));
    end
end

Data = 

      Data: [1x1 struct]
         a: 1
         b: 2.2000
         c: 3.4000
     index: 10
     model: {'336F'}
    serial: {'WTZ00151'}

So if I run this in a loop, for i = 1:5, Data should look like this:

Data = 

      Data: [1x1 struct]
         a: [1 1 1 1 1]
         b: [1x5 double]
         c: [1x5 double]
     index: [10 10 10 10 10]
     model: {1x5 cell}
    serial: {1x5 cell}

Any ideas on how to code the for loop?

2) Since there are too many variables in the workspace & I have a long list of variables that needs storing, instead of using who to save ALL variables to the structure (and then filtering out the unwanted), how could I use a list of variable names (imported from a text file: NameList) to call out what needs to be stored? Using the variable name from NameList does not call out the structure values.

Much appreciated,

Solution

It's not immediately clear what part of your code actually is creating your data structure. There are several ways to create a struct from your array of variable names.

One way is to save the relevant variables to a file and load them back into a struct

save('tmp.mat', NameList{:});
Data = load('tmp.mat');

Another option (not recommended) is to use eval

for k = 1:numel(NameList)
    Data.(NameList{k}) = eval(NameList{k});
end

As far as storing data from multiple iterations, I personally would recommend storing the data into an array of struct rather than a struct of arrays. You should be able to store each Data instance in an array using k as an index as shown below:

allData(k) = Data;

If you decide you really want a struct of arrays, you can always convert it afterwards.

fields = fieldnames(allData);

output = struct();

for k = 1:numel(fields)
    % Try to just concatenate the values together
    try
        values = [allData.(fields{k})];

    % If that failed, concatenate them within a cell array
    catch
        values = {allData.(fields{k})};
    end

    % Store this in a single output struct
    output.(fields{k}) = values;
end