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

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

[Stephen23]

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.

Answer 1

[Voss]

% 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              

[Mustafa Sobhy]

Thanks a lot, it worked.

But I need the matricies with their original file names not matrix_1, matrix_2 and so on

[Image Analyst]

@Mustafa Sobhy then evidently you overlooked my answer below.

[Voss]

OK (this assumes that the file names are valid variable names - if not, you'll get an error):

% csv_location = 'path\to\your\csv\files';
csv_location = '';

files = dir(fullfile(csv_location,'*.csv'));
for ii = 1:numel(files)
    [~,fn] = fileparts(files(ii).name);
    assignin('base',fn,readmatrix(fullfile(csv_location,files(ii).name)));
end
whos()

  Name                                  Size            Bytes  Class     Attributes

  a_file_containing_a_matrix            2x3                48  double              
  another_file_containing_a_matrix      3x4                96  double              
  ans                                   1x55              110  char                
  csv_location                          0x0                 0  char                
  files                                 2x1              1974  struct              
  fn                                    1x32               64  char                
  ii                                    1x1                 8  double              

[Stephen23]

"But I need the matricies with their original file names not matrix_1, matrix_2 and so on"

That is:

1. impossible, because variable names cannot have period characters in them
2. very bad data design, because you force yourself into writing slow, complex, inefficient code that is buggy and difficult to debug. Dynamically accessing variable names is not recommended.
3. not required, because you can very efficiently access the imported file data and also the file meta-data (e.g. filenamdes) very simply by using very basic indexing, just as _ already showed you.

What _ showed you with

files(ii).data

to store the data is much simpler and more efficient than what you are trying to do.

[Image Analyst]

@Stephen is referring to _(no name)'s first snippet, not the second snippet with assignin() and dynamically named variables. Again, see my answer and read the FAQ.

[Mustafa Sobhy]

Thanks so much

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

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

[Image Analyst]

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

Answer 2

[Image Analyst]

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