import multiple csv files in matlab

I am trying to import several csv files and compact all of them in a single variable called "data".

The csv files are 2D images (files include only numbers - no headers. I want to make a stack of these 2D images and create a 3D volume. All images have the same x- and y-dimension (i.e. same number of columns and rows).

I came across with this post https://uk.mathworks.com/matlabcentral/answers/129127-how-do-i-import-csv-files-using-csvread

Below it's the code I used:

d=dir('/Users/Desktop/csv/2Dimage_*.clv');   
n=length(d); 

data=cell(1,n);     
for i=1:n
  data(i)=csvread(d(i).name);  
end
data=cell2mat(data);

I tried to check the dimensions of the data but I don't get what I expected. I was expecting a 3D array but I got the following

ans =
     0     0

Can someone help with this please?

[Guillaume]

The code you've written will not produce a 3D array, only a 2D array of images stacked horizontally. That is trivially fixed however.

More troubling is that your result would imply that data is completely empty and hence that nothing was read. How did you "check the dimensions of the data"?

Answer 1

[Guillaume]

A simpler version of your code, that will produce a 3D array instead of stacking the images horizontally:

folder = ''/Users/Desktop/csv';
dircontent = dir(fullfile(folder, '2Dimage_*.csv'); 
images = arrayfun(@(f) csvread(fullfile(folder, f.name)), dircontent, 'UniformOutput', false);
image = cat(3, images{:});  %assumes all images are the same size. Otherwise will error

[Mar]

I still have the same problem. One thing that I've noticed is that my files have the extension .csv, i.e. 2Dimage_1.csv, 2Dimage_1.csv etc etc. I think the problem starts from the very first line when I am trying to import the data. When I tried to test the size of dircontent I got ans = 0 1

I changed the first line to dircontent = dir('/Users/Desktop/csv/2Dimage_*.csv'); and I got ans = 19 1. Although it's reading the data this way I got the error:

Error using csvread (line 35) File not found.

Error in mult_csv>@(f)csvread(f.name)

Error in mult_csv (line 11) images = arrayfun(@(f) csvread(f.name), dircontent, 'UniformOutput', false);

[Guillaume]

Well, looking for files with extension clv or files with extension csv is of course not going to return the same set of files.

The error is because csvread needs to look for the files in the correct folder rather than the current one. I overlooked that. It's easily fixed. Answer updated.

[Mar]

Great, now it works fine! Thank you a lot for your help :)

[Mar]

OK, so there is a problem still. The data import fine, are stack all together in the array image but are not in the right order. Seems they are allocated randomly. How can I make them stuck in ascending order? i.e. 0,1,2,3, etc

K>> dircontent.name

ans =

      'file_0.csv'

ans =

      'file_1.csv'

ans =

      'file_10.csv'

ans =

      'file_11.csv'

ans =

      'file_12.csv'

ans =

      'file_13.csv'

ans =

      'file_14.csv'

ans =

      'file_15.csv'

ans =

      'file_16.csv'

ans =

      'file_17.csv'

ans =

      'file_18.csv'

ans =

      'file_19.csv'

ans =

      'file_2.csv'

ans =

      'file_3.csv'

ans =

      'file_4.csv'

ans =

      'file_5.csv'

ans =

      'file_6.csv'

ans =

      'file_7.csv'

ans =

      'file_8.csv'

ans =

      'file_9.csv'

[Stephen23]

@Mar: download and use my FEX submission natsortfiles. Its online documentation, the HTML help, and Mfile help all contain plenty of examples. Probably you would put the names into a cell array:

names  = natsortfiles({dircontent.name});
images = cellfun(@(name) csvread(fullfile(folder, name)), names, 'Uni',0);

[Mar]

Thanks a lot!! All sorted now :)