MATLAB: How to concatenate variables from the workspace with a constant part in their name

variables

I´d like to find some variables and concatenate their values in a single array. These variables share the start of their name (false_onsets_). Things get complicated because for each subject in my experiment, the variables may or may not exist. So I want to concatenate all variables that exist.
To create the variables (false_onsets_), I use the following code:
if ~isempty(listen_false_index)
      for ii=1:length(listen_false_index)
          false_onsets_lis (1,ii)=onsets{1,1} (1,listen_false_index(ii));
      end
      false_duration_lis=zeros(1,length(listen_false_index));
  end
    if ~isempty(sing_along_false_index)
        for jj=1:length(sing_along_false_index)
            false_onsets_singa(1,jj)=onsets{1,1} (1,sing_along_false_index(jj));
        end
         false_duration_singa=zeros(1,length(sing_along_false_index));
    end
    if ~isempty(sing_memo_false_index)
        for kk=1:length(sing_memo_false_index)
            false_onsets_singm(1,kk)=onsets{1,1} (1,sing_memo_false_index(kk));
        end
        false_duration_singm=zeros(1,length(sing_memo_false_index));
    end
    if ~isempty(baseline_false_index)
        for ll=1:length(baseline_false_index)
            false_onsets_base(1,ll)=onsets{1,1} (1,baseline_false_index(ll));
        end
        false_duration_base=zeros(1,length(baseline_false_index));
    end
I tried using who but this just creates a cell with the names of the variables and not its value.
Any alternative idea for how this could be achieved?
Thank you in advance.
Best, Noelia

Best Answer

"Any alternative idea for how this could be achieved?"
Yes: simply avoid getting into the situation where you need to access variable names dynamically. Accessing variable names is slow, complex, buggy, and hard to debug. Beginners access variable names dynamically in order to force themselves into writing slow, complex code. Read this to know why:
https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval
There are two main ways that beginners want to access variable names dynamically, i.e. how they get lots of variables into the workspace:
  1. creating variables in a loop or from user input.
  2. loading variables from a .mat file or similar.
You do not describe which of these you used to get that data into the workspace, but I suspect that it you loaded them from a .mat file. If this is the case, then you can trivially load into an output variable (which is a scalar structure) and avoid the whole problem:
S = load(...);
N = fieldnames(S);
idx = strncmp(N,'false_onsets_',13);
for k = find(idx)
    S.(N{k})
end
Or you could load only those variables in the first place by using the optional argument regular expression:
S = load(...,'-regexp','^false_onsets_')
Simpler, neater, more efficient code through better code design: do NOT access variable names dynamically.
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