create unique output variable name based on input variable name in matlab

Question

I am making a program in matlab for data analysis of some biomedic data I collected. The calculations are really easy yet repetitive, hence my interest in writing a small program. I have one matric (200 x 99) per patient, stored in a variable with the name of the patient. I created a function that results in an output variable (finalresult) containing everything I need from this patiënts matrix.

I would really like this output variable to carry the name of my input variable. That way I can simply call the function for each patient separately and afterwards harvest a list of variables in the workspace instead of having to manually change the name of the output variable after each function call.

I hope you understand what I would like to achieve. This is the simplified example of my code:

function [ finalresult] = total_analysis( patientname)
    first = patientname(:,1)*2;
    second = first;
    finalresult = vertcat(first,second);
end

=> the output variable name is always finalresult

BUT I would like it to be a "unique other" output variablename, preferably finalresult_patientname or patientname

Umm... The name of the output variable in the function is irrelevant as far as the caller is concerned. What are you trying to do at your call site? — Edric, Nov 29 '12 at 22:26
As Edric suggests, the names used to define the function don't have to be used to call it. One call might be `patient1_result=total_analysis(patient1);`. That's the whole point of a function. No renaming necessary. — Peter, Nov 29 '12 at 22:51
Have you considered using a cell-array to store the results and access them by index instead of having several different variables? Could be more handy, especially if those data will be used for further processing. — Cavaz, Nov 29 '12 at 22:53
@Batsu +1. This seems easiest to me also. Easier even than structures. Let `N` denote number of patients. You would only need three variables: `PatientName` - a N*1 cell array of strings, where each cell stores a patients name. `PatientData` - a N*1 cell array where each cell stores a patients data matrix. `PatientResult` - a N*1 cell array where each cell stores the result of the functions analysis. To create `PatientResult` you just loop over `PatientData` and call your function for each element, storing the output in the corresponding element of `PatientResult`. — Colin T Bowers, Nov 30 '12 at 01:27

score 1 · Answer 1 · answered Nov 29 '12 at 21:08

1

why not return a struct with the result and patient name?

function [ finalresult] = total_analysis( patientname)
    first = flexion(:,1)*2;
    second = first;
    finalresult.data = vertcat(first,second);
    finalresult.name = patientname;
end

answered Nov 29 '12 at 21:08

Will Faithfull

1,868
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I still end up with the same problem this way -> the output variable is now structured and contains a name + data subvariable, but it's name is still finalresult. When I call the function for the next patients matrix, then the previous results are replaced by the next patients analysed data :s – user1864405 Nov 29 '12 at 21:37
ok, then your naming needs to take place outside the function. So where you name the workspace variable ie `patient1_finalresult = total_analysis(patient)` is where the renaming should take place. You could name a workspace variable dynamically by using [`eval`](http://www.mathworks.co.uk/help/matlab/ref/eval.html) and modifying the expression string – Will Faithfull Nov 29 '12 at 21:42

score 1 · Answer 2 · answered Nov 29 '12 at 21:09

1

I would suggest using a structure array in matlab that stores all your data in a single variable:

    s(1).name    = 'Jane';                      % Store patient's name here as a string
    s(1).data    = janesData;                   % Store patient's data
    s(1).result  = total_analysis( s(1).data )  % Store the analyzed data

    s(2).name    = 'John';                      % Store patient's name here as a string
    s(2).data    = johnsData;                   % Store patient's data
    s(2).result  = total_analysis( s(2).data )  % Store the analyze

And so on for all of your patients' data. Then you can simply use s(i) to get all the variables associated with with the i_th patient.

answered Nov 29 '12 at 21:09

jerad

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This is a fair suggestion, but I think that renaming the output variable after each function will be less work then storing everything in separate structure arrays. I just thought there was a simple command or something to turn the name of a variable in a string and use this to name another variable with. I am new to matlab but eager to learn :) Thanks to everyone for the help – user1864405 Nov 29 '12 at 22:42
@user1864405 Do you already have all the patient names stored as strings in a single variable? – jerad Nov 29 '12 at 22:57

score 1 · Answer 3 · answered Nov 30 '12 at 07:01

This is clearly bad design, but you can use the evalin function. Something like the following:

cmd = sprintf('result_%s = %f', suffix, result);
evalin('caller', cmd);

Then you call your function myfunc without assigning its output.

Again, this is not a good idea since most users will not expect this behavior. Functions are expected to return results while letting the caller assign the result to any variable he chooses to.

Good for small hacks and not for long-lasting code.

score 0 · Answer 4 · answered Nov 29 '12 at 21:46

0

Further to your comment, here's an example of using eval to dynamically name a workspace variable:

>> string = 'patient1';
>> eval(strcat(string, '_finalresult = 200'))

patient1_finalresult =

   200

answered Nov 29 '12 at 21:46

Will Faithfull

1,868
13
20

create unique output variable name based on input variable name in matlab

4 Answers4