How to save a function output to a variable with variable name changing dynamically?

I have two folders in two different paths. These two folders contain .csv data files. I want to load these .csv data files from each folder and fun PCA on them. I want to save output variable in a format so that I can keep track that from which data folder I imported those .csv files.

For example, in my code below, I have Data1 and Data2 folders containing these .csv files. In the first iteration of for loop, I will like to load .csv files from folder Data1, and save output variable from pca function as Data1_Name_PCA. For the second iteration, I will like to save the output variable from pca as Data2_Name_PCA, and so on.

Here _PCA is fixes. Only Data1_Name and Data2_Name should change for each iteration.

My code works fine, but I am trying to figure out how to save output of PCA on these dynamically changing names.

For testing my code below, you can use arbitrary .csv files.

Path1 = 'C:\Users\Anonymous\MATLAB\Data1';
Path2 = 'C:\Users\Anonymous\MATLAB\Data2';

DataFiles1 = dir(fullfile(Path1, '*.csv'));
DataFiles2 = dir(fullfile(Path2, '*.csv'));

Filename1 = {DataFiles1.name};
Filename2 = {DataFiles2.name};

filename = {Filename1, Filename2};

[rows, cols] = size(filename);

for i = 1:cols  
    data1 = importdata(filename{i}{1});
    data2 = importdata(filename{i}{2});

    data1_Name = filename{i}{1}(1:end-4);
    data2_Name = filename{i}{2}(1:end-4);

    [data1_Name_PCA, eigVec1_PCA, lambda1_PCA] = pca(data1, 3);
end

[Stephen23]

Do NOT do this. The MATLAB documentation specifically warns against doing exactly this: "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not use the array processing power of MATLAB and is not recommended. The preferred method is to store related data in a single array."

source: https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

http://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

[Walter Roberson]

Please do not close questions that have an Answer.

The output you desire is possible. We firmly recommend against it.

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

Answer 1

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

[hello_world]

@ Walter Roberson so is there any alternate way to achieve what I am trying to do?

[Walter Roberson]

You can use dynamic field names under a common variable.

[~, basename1] = fileparts(filename{i}{1});
fieldname1 = matlab.lang.makeValidName([basename1 '_PCA']);

[all_data.(fieldname1), ...] = ....

[Stephen23]

" is there any alternate way to achieve what I am trying to do?"

The simplest and most efficient way is to use indexing. Indexing is simple, very efficient, and very easy to debug (unlike what you are trying to do). Just do something like this:

N = numel(filename);
name = cell(1,N);
data = cell(1,N);
...
for k = 1:N
    ...
    name{k} = ...
    data{k} = ...
end

Simpler, neater, more efficient code through better code and data design. This is not the first time you have been given the advice to avoid dynamic variable names:

https://www.mathworks.com/matlabcentral/answers/284681-matlab-cannot-call-or-index-into-a-temporary-array-in-for-loop#answer_222550

[hello_world]

@ Walter Roberson: thank you for your feedback. I will try this code and get back to you. It would be nice if you put your code lines in my code above so that there was no confusion. This way I will see the complete example.

[hello_world]

@Stephen Cobeldick: thank you for your feedback. I will try this code and get back to you. It would be nice if you put your code lines in my code above so that there was no confusion. This way I will see the complete example.

[Walter Roberson]

Replace your line

      [data1_Name_PCA, eigVec1_PCA, lambda1_PCA] = pca(data1, 3);

with

[~, basename1] = fileparts(filename{i}{1});
fieldname1 = matlab.lang.makeValidName([basename1 '_PCA']);

[all_data.(fieldname1), eigVec1_PCA, lambda1_PCA] = pca(data1, 3);

[hello_world]

@Walater Roberson: I checked. So I will have a variable all_data.(fieldname1) which will have out put of PCA function. However, I want this variable name to change so that I can use it further. For example, if I want to plot it:

plot(data1_Name_PCA(:,1), data1_Name_PCA(:,2), 'r')

Or I misunderstand your answer?

By the way, for simplicity I asked that I wanted to change only the first variable, but in fact, I will be changing all output variable names with each iteration.

[Walter Roberson]

plot(all_data.(fieldname1)(:,1), all_data.(fieldname2)(:,2), 'r')

[hello_world]

@Walter Roberson: Yeah ok, it will work. But I really wanted to have an output variable as data1_Name_PCA rather than all_data.(fieldname1). Let me see if some other possibility before accepting your answer.

I appreciate your help though!

[Walter Roberson]

If you follow the link above, you will find links to information on how it is possible to create variable names dynamically. However, we really do not recommend it.

[Stephen23]

"But I really wanted to have an output variable as..."

Sure, we understand what you want. And we are advising you, that that approach is not recommended by any MATLAB experts, experienced MATLAB users, or by the MATLAB documentation. Wanting code to do a particular thing does not correlate with it being a good idea, nor with it even being tractable at all, which is why we are giving advice on how to write better code: https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval#comment_577030