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stringmatlabmatrixfile-iotext-files
Maddy
Maddy

Reputation: 2570

How can I write strings and matrices to a .txt file in MATLAB?

I need to write data to a .txt file in MATLAB. I know how to write strings (fprintf) or matrices (dlmwrite), but I need something that can do both of them. I'll give an example below:

str = 'This is the matrix: ' ;
mat1 = [23 46 ; 56 67] ;
%fName
if *fid is valid* 
    fprintf(fid, '%s\n', str)
    fclose(fid)
end
dlmwrite(fName, *emptymatrix*, '-append', 'delimiter', '\t', 'newline','pc')
dlmwrite(fName, mat1, '-append', 'newline', 'pc')

This works okay, but with a problem. The first line of the file is:

This is the matrix: 23,46

Which is not what I want. I want to see:

This is the matrix:
23 46
56 67

How can I solve this? I can't use a for loop and printf solution as the data is huge and time is an issue.

Upvotes: 9

Views: 84932

Answers (4)

mlanzero
mlanzero

Reputation: 139

I ran into a similar situation adding a header to a csv. You can use dlmwrite with -append to add a single line by setting your delimiter equal to '' as shown below.

str = 'This is the matrix: ';      %# A string
mat1 = [23 46; 56 67];             %# A 2-by-2 matrix
fName = 'str_and_mat.txt';         %# A file name
header1 = 'A, B'
dlmwrite(fName, str, 'delimiter', '')
dlmwrite(fName, header1, '-append', 'delimiter', '')
dlmwrite(fName, mat1, '-append','delimiter', ',')

This produces the following:

This is the matrix: 
A, B
23,46
56,67

Upvotes: 1

gnovice
gnovice

Reputation: 125854

I think all you have to do to fix your problem is add a carriage return (\r) to your FPRINTF statement and remove the first call to DLMWRITE:

str = 'This is the matrix: ';      %# A string
mat1 = [23 46; 56 67];             %# A 2-by-2 matrix
fName = 'str_and_mat.txt';         %# A file name
fid = fopen(fName,'w');            %# Open the file
if fid ~= -1
  fprintf(fid,'%s\r\n',str);       %# Print the string
  fclose(fid);                     %# Close the file
end
dlmwrite(fName,mat1,'-append',...  %# Print the matrix
         'delimiter','\t',...
         'newline','pc');

And the output in the file looks like this (with tabs between the numbers):

This is the matrix: 
23  46
56  67


NOTE: A short explanation... the reason for needing the \r in the FPRINTF statement is because a PC line terminator is comprised of a carriage return followed by a line feed, which is what is used by DLMWRITE when the 'newline','pc' option is specified. The \r is needed to ensure the first line of the matrix appears on a new line when opening the output text file in Notepad.

Upvotes: 24

Charles L.
Charles L.

Reputation: 6275

You don't need the empty matrix call. Try this code:

str = 'This is the matrix: ' ;
mat1 = [23 46 ; 56 67] ;
fName = 'output.txt';
fid = fopen('output.txt','w');
if fid>=0
    fprintf(fid, '%s\n', str)
    fclose(fid)
end
dlmwrite(fName, mat1, '-append', 'newline', 'pc', 'delimiter','\t');

Upvotes: 5

Andrew Janke
Andrew Janke

Reputation: 23858

You've got two dlmwrite() calls, the first on an empty matrix, and the second one is missing the 'delimiter' option. What happens if you add it to the second call?

Upvotes: 2

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