Using writetable in a for loop to create new txt/csv files for each step

Hi,

I am basically going through csv files and adding a collumn on which is the running cumlitive sum of 144 entries.

I then want to write a new vairable for each table. I have been using the writetable function but can not seem to get it working with errors regarding the filename. Below is my code without the writetable line, could anyone assist with what I should write to export each iteration as a csv or txt file

 % Get the list of all .mat files in current directory
f=dir('*.csv');

for i=1:length(f)
    % Read the input file name one-by-one. Load variables to 's'
    % It's a structure NOTE to self
    x=readtable(f(i).name);
    % Get the field names of above structure
    fld=fieldnames(x);
    % Read actual table
    t=x.(fld{1});
    
    % This loop creates a range of rows to be filtered out
    for j=1:height(x)
        %%add collumn for cumulitve sum  
        x.AOI=movsum(x.exceedConst,144);
        
    end
end

[dpb]

The above code makes no sense -- readtable will return a table object, not a struct

To make any sense of it, attach one or two of the .csv files -- use the paperclip icon.

[Patrick Lonergan]

the above code I had edited an old script, but I have reviewed it and it can be done much simpler. I have attached one of 200 csv fies that the script below reads;

 % Get the list of all .mat files in current directory
f=dir('*.csv');

for i=1:length(f)
    % Read the input file name one-by-one. Load variables to 's'
    x=readtable(f(i).name);
     %%add collumn for cumulitve sum  
        x.AOI=movsum(x.exceedConst,144);
        
  
end

As above I want to use writetable to save each iteration

[Ive J]

% if you wanna write the 'whole' modified table to a new file
for i = 1:numel(f)
    % do whatever
    
    newfile = ['file', num2str(i), '.csv']; 
    writetable(x, newfile);
end

% or if you wanna write only 'AOI' to a new file
for i = 1:numel(f)
    % do whatever
    
    newfile = ['file', num2str(i), '.csv']; 
    writetable(x(:, end), newfile); 
end

[Patrick Lonergan]

Thanks, great help worked perfectly

Answer 1

[Scott MacKenzie]

Under the assumption your code is working fine except for the filename issue, here's what I suggest. Use this to create a new filename for the output file. Add the line just before writing to the file:

fNew = insertBefore(f(i).name, '.csv', strcat('_', string(i)));

fNew is the name of the file to write to via writetable. It's the name of the file being processed except adding '_n' just before '.csv'. The value of n is the value of i in the loop.

Answer 2

[Mathieu NOE]

hello

seems you were one inch or even less to a solution .

Now it was a bit unclear to me if you wanted to save the new table in the original file or to another file

basically the two options are available here :

 clc
 clearvars
 
 % Get the list of all .mat files in current directory
f=dir('Alarm*.csv');

for i=1:length(f)
    % Read the input file name one-by-one. Load variables to 's'
    x=readtable(f(i).name);
     %%add collumn for cumulitve sum  
    x.AOI=movsum(x.exceedConst,144);
    
    % write new table in output file 
%     writetable(x,['out' num2str(i) '.csv']); % debug line : to not
%     overwrite input data file => saved in different file name
    writetable(x,f(i).name); % this will overwrite input data file
        
  
end

[Patrick Lonergan]

Perfect, thanks this works great