How to open csv files as separate numeric matrices from a certain directory?

Question

Mustafa Sobhy 2022-2-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1648975-how-to-open-csv-files-as-separate-numeric-matrices-from-a-certain-directory

编辑： Stephen23 2022-2-25

采纳的回答： Voss

I have many csv files in a folder and I need to open all as separate numeric matrices in workspace.

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Stephen23 2022-2-25

编辑：Stephen23 2022-2-25

Don't make your code slow, complex, and inefficient with dynamically named variables:

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

The content of a cell array (as the accepted answer shows) are already separated arrays.

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Answer 1

Voss 2022-2-13

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https://ww2.mathworks.cn/matlabcentral/answers/1648975-how-to-open-csv-files-as-separate-numeric-matrices-from-a-certain-directory#answer_895130

在 MATLAB Online 中打开

% csv_location = 'path\to\your\csv\files';
csv_location = '';
files = dir(fullfile(csv_location,'*.csv'));
for ii = 1:numel(files)
    files(ii).data = readmatrix(fullfile(csv_location,files(ii).name));
end

Now the matrices are in the 'data' fields of the 'files' stucture array. You can access them like:

files(1).data
ans = 2×3
     1     2     3
     4     5     6
files(2).data
ans = 3×4
     1     2     3     4
     5     6     7     8
     9    10    11    12

If you really want to make separate matrix variables in the workspace, you can do this instead:

files = dir(fullfile(csv_location,'*.csv'));
for ii = 1:numel(files)
    assignin('base',sprintf('matrix_%d',ii),readmatrix(fullfile(csv_location,files(ii).name)));
end
whos('matrix_*')
  Name          Size            Bytes  Class     Attributes

  matrix_1      2x3                48  double              
  matrix_2      3x4                96  double              

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Mustafa Sobhy 2022-2-25

Thanks so much

Can I import the second column only from all files using this command?

readmatrix(path2mat,delimitedTextImportOptions('DataLines',[Inf,1]))

Image Analyst 2022-2-25

@Mustafa Sobhy readmatrix() has a 'Range' option where you can specify the second column.

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Answer 2

Image Analyst 2022-2-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1648975-how-to-open-csv-files-as-separate-numeric-matrices-from-a-certain-directory#answer_895125

编辑：Image Analyst 2022-2-13

在 MATLAB Online 中打开

See the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

% Specify the folder where the files live.
myFolder = pwd; % or 'C:\Users\yourUserName\Documents\My Pictures'; or wherever they are
% 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 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 an array with csvread() or readmatrix() or importdata().
    data = imread(fullFileName);
end

By the way, you should process each set of data inside the loop. If you will need the data later, you can put it into a multidimensional array or a cell array.

https://matlab.fandom.com/wiki/FAQ#What_is_a_cell_array.3F

It's a very bad idea to give each data set its own unique name. Why? See the FAQ:

https://matlab.fandom.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2C_A10_in_a_loop.3F