MATLAB Answers


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

Asked by Ravnalis Michael on 30 Jul 2019
Latest activity Commented on by Walter Roberson
on 31 Jul 2019
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{:} );
the "num2cell(d1(1:end,7))" is the new column that i want to add.
Thanking in advance


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1 Answer

Answer by Kojiro Saito on 31 Jul 2019
 Accepted Answer

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,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 ?
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)
Error in test_v2_pro (line 103)
Do you have any idea about the command should I use in order to finish it with success?
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.

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