Adding a new column to an existing csv file via Matlab.

Hello,

I have a question. I want to add a new column to an existing filename via commants in matlab. The existing file (called 'filename1' ) has 22 columns and 400 rows. I ve created the column that I want to add , whis has 400 rows too. The final output i want to have is a csv file with 23 columns and 400 rows. I used these commands , without results:

M1 = [filename1, num2cell(d1(1:end,7))].';  %transpose important 

fid = fopen('gtm.csv','wt');
fprintf(fid,'%15s %.6f\n',M1{:} );

fclose(fid);

the "num2cell(d1(1:end,7))" is the new column that i want to add.

Thanking in advance

Answer 1

[Kojiro Saito]

You can do it easily with writetable.

Here is an example.

filename1 = 'existingData.csv';
% Read the CSV as a table
t = readtable(filename1);

% Add a new column to the end of the table
numOfColumn = size(t, 2);
newCol = num2cell(d1(1:end,7)); % Your new column
t.(numOfColumn+1) = newCol;

% Change column name if needed
t.Properties.VariableNames{numOfColumn+1} = 'newCol';

% Write to CSV file
writetable(t, 'new.csv')

[Walter Roberson]

Or you could simplify a bit by using

filename1 = 'existingData.csv';
% Read the CSV as a table
t = readtable(filename1);
% Add a new column to the end of the table
t.newCol = d1(1:end,7); % Your new column
% Write to CSV file
writetable(t, 'new.csv')

WIth R2019a or later in the special case that the rows are all numeric, then

filename1 = 'existingData.csv';
% Read the CSV as an array
t = readmatrix(filename1);
% Add a new column to the end of the array
t(:,end+1) = d1(1:end,7); % Your new column
% Write to CSV file
writematrix(t, 'new.csv')

[Ivan Mich]

Walter Roberson, Kojiro Saito Thank you for your answers but there is a problem...

ok, I am using these commands :

fid = fopen('results.txt','wt');

writetable(CT{:},'tabledata.txt')

fclose(fid);

and in the command window shows these:

Error in writetable (line 106)

write(a,filename,varargin{:})

Error in test_v2_pro (line 118)

writetable(CT{:},'tabledata.txt')

Do you know something about?

[Walter Roberson]

You would not fopen: writetable does its own file operations.

You should not be passing CT{:} and instead should be passing a table object. Not a cell array.

[Ivan Mich]

Walter Roberson,Excuse me , but honestly I do not understand what do you mean by saying:

"You should not be passing CT{:} and instead should be passing a table object. Not a cell array."

Could you explain me ?

[Ivan Mich]

Walter Roberson,Basically i believe that the main problem is in the command writetable, because command window shows me these:

Undefined function 'write' for input arguments of type 'cell'.

Error in writetable (line 106)

write(a,filename,varargin{:})

Error in test_v2_pro (line 103)

writetable(MI{:},'tabledata.txt')

Do you have any idea about the command should I use in order to finish it with success?

[Walter Roberson]

We are telling you that you should stop working with xlsread and should use readtable() to read your data, and use the command we show to add a new column to the table and then writetable the results.

%read file 
t = readmatrix('filename1.csv');
% Add a new column to the end of the array
t(:,end+1) = d1(:,7); % Your new column
% Write to CSV file
writematrix(t, 'tabledata.txt')

Notice no xlsread, no cell array.