I have a text file with 10 lines and 5 columns. I need to write a value (zero or one) at the end of each row, that is, in the last column of each row. How can i do this?

I have a text file with 10 lines and 5 columns. I need to write a value (zero or one) at the end of each row, that is, in the last column of each row. How can i do this? I'm trying to write in a specific row and column. I was trying to use this: dlmwrite(filename,M,delimiter,row,col)

My file:

1.6 0.81 7.4 -4.7 -3.6

-7.6 8.8 2.9 -0.41 2.8

0.89 2.9 0.88 4.4 0.45

9.9 -5.6 -7.9 -7.8 -8.7

-1.9 -1 -2.7 5.3 2.6

5.4 8.7 9.5 -6.2 -7.2

3.9 -8.1 0.51 0.61 7.2

-0.3 -2.1 3.4 4.8 0.4

-3 -7 1.7 -4.8 -9.1

5.1 -5.1 -1.2 3.8 -2.8

Answer 1

[Chris]

dlmwrite is deprecated, though you could use it in a similar fashion as below:

fname = 'filename.txt';
outname = 'out.txt';
M = readmatrix(fname);
M(:,end+1) = randi(2,10,1)-1

M = 10×6

1.6000 0.8100 7.4000 -4.7000 -3.6000 1.0000 -7.6000 8.8000 2.9000 -0.4100 2.8000 1.0000 0.8900 2.9000 0.8800 4.4000 0.4500 1.0000 9.9000 -5.6000 -7.9000 -7.8000 -8.7000 1.0000 -1.9000 -1.0000 -2.7000 5.3000 2.6000 1.0000 5.4000 8.7000 9.5000 -6.2000 -7.2000 1.0000 3.9000 -8.1000 0.5100 0.6100 7.2000 1.0000 -0.3000 -2.1000 3.4000 4.8000 0.4000 0 -3.0000 -7.0000 1.7000 -4.8000 -9.1000 0 5.1000 -5.1000 -1.2000 3.8000 -2.8000 1.0000

writematrix(M,outname,'delimiter','space');

If you want integer formatting for the ones/zeros, you could use tables:

M = readtable(fname);
endbits = randi(2,10,1)-1;
M(:,end+1) = table(endbits)

M = 10×6 table
    Var1    Var2    Var3    Var4     Var5    Var6
    ____    ____    ____    _____    ____    ____

     1.6    0.81     7.4     -4.7    -3.6     1  
    -7.6     8.8     2.9    -0.41     2.8     0  
    0.89     2.9    0.88      4.4    0.45     0  
     9.9    -5.6    -7.9     -7.8    -8.7     0  
    -1.9      -1    -2.7      5.3     2.6     0  
     5.4     8.7     9.5     -6.2    -7.2     1  
     3.9    -8.1    0.51     0.61     7.2     1  
    -0.3    -2.1     3.4      4.8     0.4     0  
      -3      -7     1.7     -4.8    -9.1     0  
     5.1    -5.1    -1.2      3.8    -2.8     1  

writetable(M,outname,'WriteVariableNames',false,'delimiter','space');

Edit: If you want to change one line at a time, one option is to use a cell array.

fname = 'filename.txt';
M = readcell(fname);

% Fix missing
mask = cellfun(@ismissing, M);
M(mask) = {[]};

% Write a value
M{3,end+1} = 1

M = 10×6 cell array
    {[ 1.6000]}    {[ 0.8100]}    {[ 7.4000]}    {[-4.7000]}    {[-3.6000]}    {0×0 double}
    {[-7.6000]}    {[ 8.8000]}    {[ 2.9000]}    {[-0.4100]}    {[ 2.8000]}    {0×0 double}
    {[ 0.8900]}    {[ 2.9000]}    {[ 0.8800]}    {[ 4.4000]}    {[ 0.4500]}    {[       1]}
    {[ 9.9000]}    {[-5.6000]}    {[-7.9000]}    {[-7.8000]}    {[-8.7000]}    {0×0 double}
    {[-1.9000]}    {[     -1]}    {[-2.7000]}    {[ 5.3000]}    {[ 2.6000]}    {0×0 double}
    {[ 5.4000]}    {[ 8.7000]}    {[ 9.5000]}    {[-6.2000]}    {[-7.2000]}    {0×0 double}
    {[ 3.9000]}    {[-8.1000]}    {[ 0.5100]}    {[ 0.6100]}    {[ 7.2000]}    {0×0 double}
    {[-0.3000]}    {[-2.1000]}    {[ 3.4000]}    {[ 4.8000]}    {[ 0.4000]}    {0×0 double}
    {[     -3]}    {[     -7]}    {[ 1.7000]}    {[-4.8000]}    {[-9.1000]}    {0×0 double}
    {[ 5.1000]}    {[-5.1000]}    {[-1.2000]}    {[ 3.8000]}    {[-2.8000]}    {0×0 double}

% Write the file
writecell(M,fname,'delimiter','space');

The output:

1.6 0.81 7.4 -4.7 -3.6

-7.6 8.8 2.9 -0.41 2.8

0.89 2.9 0.88 4.4 0.45 1

9.9 -5.6 -7.9 -7.8 -8.7

-1.9 -1 -2.7 5.3 2.6

5.4 8.7 9.5 -6.2 -7.2

3.9 -8.1 0.51 0.61 7.2

-0.3 -2.1 3.4 4.8 0.4

-3 -7 1.7 -4.8 -9.1

5.1 -5.1 -1.2 3.8 -2.8

[Alex Muniz]

In fact, I have a file with n lines and I need to read a line, perform an operation and, depending on the result, write one or zero in the last column of that line. I need to perform this procedure for all lines in this file.

[Chris]

@Alex Muniz I added an option to the end of my original post.

Note, for all of these options, the entire file is read in and written out. For very large files, other options may need to be considered.

[Alex Muniz]

First I would like to thank you for your help. The file I intend to work on has between 5 and 30 thousand lines, would this procedure apply to a file of this size?

[Chris]

@Alex Muniz

A 30,000 x 6 cell array takes up 20 MB in memory, which is small potatoes when you're working with GB of RAM.

Writing such a file to my SSD takes ~9 s, and reading it takes 2. An old drive might be a bit slower, but I think the speed is mostly limited by whatever the writecell function is doing in the background.

A typical program flow would be to load the file into Matlab at the start of your program and work on it in memory, then write it out ("save" the file) when you're ready to close the program. Working in RAM is lightning fast compared to reading/writing to hard disk. If you can deal with the long read/write times at the beginning and end, that's what I would do (perhaps display 'Please wait...' while loading/saving).

If, for some reason, you still want to write bits randomly to the hard drive and not keep the file in memory, then we're in an area I don't know much about. Off the top of my head, a tall array might be appropriate in that case. Or a database.