How can I iterate through an array using a for loop?

I want to iterate through an array of file locations using a for loop.

My current code is something like this:

% Paths where the files are located
P1 = C:\Users\me\Documents\\My Info
%Find excel files in path
%Pull data
% Write into a file

Now this code works great, but now I need to do the same thing to multiple paths while maintaining efficiency. To do this, I created an array of the paths I need to iterate through. How do I use a for loop to iterate through these paths? Here is what I have so far, but my code breaks when it tries to read the path because the text is not scalar when trying to use 'dir'. Here is what I currently have:

% Paths where the files are located
P1 = C:\Users\me\Documents\\My Info
P2 = C:\Users\me\Documents\\My data
%Array of paths
Array = {'P1, P2'}
for i = 1:length(Array)
    %Find excel files in path
    %Pull data
    % Write into a file

Answer 1

[Image Analyst]

The paths need to be enclosed in single or double quotes. Then when you put them into a cell array don't use quotes there. And you need to use fullfile to construct the full path. And don't use i (the imaginary constant) as a loop iterator. Untested code:

% Paths where the files are located
P1 = 'C:\Users\me\Documents\My Info';
P2 = 'C:\Users\me\Documents\My data';
%Array of paths
Array = {P1, P2};
for k = 1:length(Array)
    thisFolder = Array{k};
    % Find all Excel files in this folder.
    filePattern = fullfile(thisFolder, '*.xls*');
    fileList = dir(filePattern)
    for f = 1 : numel(fileList)
        fullFileName = fullfile(thisFolder, fileList(f).name);
        fprintf('Processing %s.\n', fullFileName);
        % Pull data
        data = readmatrix(fullFileName);
        % Write into am output file
        baseFileName = sprintf('New %s', fileList(f).name)
        outputFileName = fullfile(thisFolder, baseFileName);
        writeMatrix(data, outputFileName);
    end
end

Also, please read the FAQ: What is a cell array

for a good explanation of how to use cell arrays and when to use braces, parentheses, and brackets.

To learn other fundamental concepts, invest 2 hours of your time here:

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Answer 2

[Stephen23]

Given an array of paths:

C = {'C:\Users\me\Documents\My Info','C:\Users\me\Documents\My data'};
F = @(p)dir(fullfile(p,'*.xlsx'));
D = cellfun(F,C,'uni',0); % or use a FOR-loop
S = vertcat(D{:}); % comma-separated list

https://www.mathworks.com/matlabcentral/discussions/tips/847976-tutorial-comma-separated-lists-and-how-to-use-them

Or assuming a small fixed number of paths:

S = [...
    dir('C:\Users\me\Documents\My Info\*.xlsx');...
    dir('C:\Users\me\Documents\My data\*.xlsx')];

Then loop over all files (including their paths!):

for k = 1:numel(S)
    F = fullfile(S(k).folder,S(k).name);
    ...etc
end

Another option might be to use a datastore:

https://www.mathworks.com/help/matlab/datastore.html

[Sergio E. Obando]

+1 to using datastore. You should not need to use a for loop if you leverage read/readall and similar to write to file.