How to write a new column in a text file?

I have a text file which already has two columns (one with pressure values, the other one with velocity values). I want to make a new column on the right side in which I add the time. If I use this code, it adds me the column, but below my existing columns. I want them to be like this: 'Pressure Velocity Time.'

string='E:\MASTER\Biofluid mechanics\WIA-Matlab-Biofluid\data2.txt';

fid=fopen(string,'a');
x=[0:0.005:.625];  %time
x=x';
fprintf(fid, '%f\n',x)
fclose(fid);

Answer 1

[Ameer Hamza]

The easiest way is to load the entire file and then save it again after adding the third column. Any other option will require you to use fseek to move row by row and write each number at a time at a specified location.

string='E:\MASTER\Biofluid mechanics\WIA-Matlab-Biofluid\data2.txt';
data = load(string); % load data in txt file
x=[0:0.005:.625];  %time
data = [data x.']; % append the third column
fid=fopen(string, 'w');
fprintf(fid, '%f\t%f\t%f\n',data(:,1), data(:,2), data(:,3));
fclose(fid)

[Cretu Ioana]

Is working, thank you!

[Ameer Hamza]

Glad to be of help.

Answer 2

[Geoff Hayes]

Cretu - when you open the file with the 'a' permission, the data will be appended to the end of the file. Since you want to add a new column to the existing data, then you may want to first import the data into MATLAB, add the new column, and then write the data back to file. For example,

filename = 'E:\MASTER\Biofluid mechanics\WIA-Matlab-Biofluid\data2.txt';
myData = importdata(filename);   % <---- or readmatrix instead
x=[0:0.005:.625];
myData = [myData ; x']; % <--- assumes same number of rows in x and myData
writematrix(myData, filename); 

If your version of MATLAB doesn't support writematrix then you may need to use fprintf or something similar.