Read multiple CSV files from different folders uing readtable

Hello

I have to read multiple csv files from differnt folders on the same editor window to plot on the same figure.

I have tried sth like this

ds1 = datastore('*.csv');

T = readall(ds1);

buit this gives data for only the currecnt directory.

I have file paths p1 , p2 and p3 for each 3 folders and i want to read thoese files from the 3 folder,

I am stuck and appreciate your help

Thank you

Answer 1

[Image Analyst]

See the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files?

% Specify the folder where the files live.
myFolder = 'C:\Users\yourUserName\Documents\My CSV Files';
% Check to make sure that folder actually exists.  Warn user if it doesn't.
if ~isfolder(myFolder)
    errorMessage = sprintf('Error: The following folder does not exist:\n%s\nPlease specify a new folder.', myFolder);
    uiwait(warndlg(errorMessage));
    myFolder = uigetdir(); % Ask for a new one.
    if myFolder == 0
        % User clicked Cancel
        return;
    end
end
% Get a list of all files in the folder, and its subfolders, with the desired file name pattern.
filePattern = fullfile(myFolder, '**/*.csv'); % Change to whatever pattern you need.
theFiles = dir(filePattern);
for k = 1 : length(theFiles)
    baseFileName = theFiles(k).name;
    fullFileName = fullfile(theFiles(k).folder, baseFileName);
    fprintf(1, 'Now reading %s\n', fullFileName);
    % Now do whatever you want with this file name,
    % such as reading it in as a table.
    thisTable = readtable(fullFileName);
end

[Bizuayehu Addisie Beyene]

I was just using this code. thank you. How can i get all values of a given variable to be printed out of the loop?

for exampole

B=data(:,3) % i need the 3rd column but all colums of the entire data ...i am geeting only the last iteration.

thank you again

[Image Analyst]

Because you left the semicolon off, that should print out the values of B to the command window. Do you not see them?

If you want to store/save them for later, you'll have to make B a matrix and give the column number, like

B(:, k) = data(:, 3); % Store 3rd column of data in k'th column of B.

[Bizuayehu Addisie Beyene]

I can see its printed on the command window... I am doing this and i have the follwoing error: K is 1 for this case...which was supposed to be length of files.... I am confused here ....

Thank you so much again

myFolder = p3;%'C:\Users\yourUserName\Documents\My Pictures';

% Get a list of all files in the folder with the desired file name pattern.

file= fullfile(myFolder, '*.CSV'); % Change to whatever pattern you need.

Files = dir(file);

B=zeros(198,1);% length(L(:,3)

for k = 1 : length(Files)

FileName = Files(k).name;

fullFileName = fullfile(Files(k).folder, FileName);

l = readtable(fullFileName);

B(:,k)=l{:,3}

end

histogram(B)

error: Unable to perform assignment because the

size of the left side is 198-by-1 and the

size of the right side is 6-by-1.

Error in seasonal_bubble_2014 (line 38)

B(:,k)=l{:,3}

Answer 2

[KSSV]

thepaths = {p1,p2,p3} ;
for i = 1:3 % loop for ech folder 
    csvFiles = dir([thepaths{i},'\*csv']) ;  % get ll csv files in the folder 
    N = length(csvFiles) ; 
    for j = 1:N  % loop for each csv file 
        csvFile = fullfile(csvFiles(j).folder,csvFiles(j).name) ;
        T = readtable(csvFile) ;
        % do what you want 
    end
end

[Bizuayehu Addisie Beyene]

I am doing this enside the loop and it works. but i want to get 'd' to be printed outside of the loop. Is it possible? I am getting only the last iteration

thank you

l = readtable(fullFileName);

d=l(:,3)

[Bizuayehu Addisie Beyene]

I copy pasted your code and its not giving me either error message or result?

paths = {p1,p2,p3} ;
for i = 1:3 % loop for ech folder 
    csvFiles = dir([paths{i},'\*csv']) ;  % get ll csv files in the folder 
    N = length(csvFiles) ; 
    for j = 1:N  % loop for each csv file 
        csvFile = fullfile(csvFiles(j).folder,csvFiles(j).name) ;
        T = readtable(csvFile) 
        % do what you want 
    end
end

[KSSV]

Check the paths......

[Bizuayehu Addisie Beyene]

the paths are correct.

[Stephen23]

"I am getting only the last iteration"

If you want to store the data from every iteration then you will need to allocate that data to an array, just as the MATLAB documentaton shows:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html

[Bizuayehu Addisie Beyene]

I want to store the values of f as shown below to make histogram. this way i am getting only the last iteration.

Any help

thank you

myFolder = p3;%

% Get a list of all files in the folder with the desired file name pattern.

file= fullfile(myFolder, '*.CSV'); % Change to whatever pattern you need.

Files = dir(file);

for k = 1 : length(Files)

FileName = Files(k).name;

fullFileName = fullfile(Files(k).folder, FileName);

l = readtable(fullFileName);

f=l{:,3};

end

histogram(f,4)

Answer 3

[Image Analyst]

You need to index f. Actually I'd use more descriptive variable names. No one wants to look at code that looks like aphabet soup.

% Get a list of all files in the folder with the desired file name pattern.
filePattern = fullfile(myFolder, '*.CSV'); % Change to whatever pattern you need.
fileList = dir(filePattern);
for k = 1 : length(fileList)
    % Read in this table.
    baseFileName = fileList(k).name;
    fullFileName = fullfile(fileList(k).folder, baseFileName);
    thisTable = readtable(fullFileName); 
    % Extract the third column only.
    column3 = thisTable{:, 3};
    % Append this column to our master vector.
    if k == 1
        allColumn3s = column3;
    else
        allColumn3s = [allColumn3s; column3]
    end
end
numBins = 4;
histogram(allColumn3s, numBins)
grid on;

If you have any more questions, then attach your data (at least 2 CSV files) with the paperclip icon after you read this:

TUTORIAL: How to ask a question (on Answers) and get a fast answer

[Bizuayehu Addisie Beyene]

works perfect! Thank you so much

[Image Analyst]

Then can you please click the "Accept this answer" link? Thanks in advance. 😃

[Bizuayehu Addisie Beyene]

I already accepted your answer !

Havea good day :)