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

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Abigail
Abigail 2024-7-30
编辑： Walter Roberson 2024-7-30
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

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采纳的回答

Image Analyst
Image Analyst 2024-7-30
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.
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更多回答（1 个）

Stephen23
Stephen23 2024-7-30
编辑：Stephen23 2024-7-30
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
  1 个评论
Sergio E. Obando
Sergio E. Obando 2024-7-30
+1 to using datastore. You should not need to use a for loop if you leverage read/readall and similar to write to file.

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