add new column into existing text file

i have 10 file and every file have 1 column data..i want to extract the column from all file and write into first file ..so, finally, in the first file, i will have ten column data..i try use load and fprint..i can load the column but when i try to write into file, the data is continues..not became as column..so, can someone help me??

Answer 1

[Walter Roberson]

You cannot add a column to a text file by opening it with 'a' (append) access. You must re-write the entire text file to have everything it had before as well as the new column.

However, if all of the data files have the same number of columns, it is easier to read all the data in first and then to write it out in one step.

[Code revised to make it much more robust]

magiclen = 6625;
magiccol = 5;
n ='average.txt';

files = dir('*.txt');

%the file average.txt might have been detected by dir() so remove it
tf = arrayfun(@(K) strcmp(n, files(K).name), 1:length(files));
files(tf) = [];

nfile = length(files);

if nfile == 0
  error('There were no files found');
end

if nfile == 1;
  warning(sprintf('Only one file found, only one column of output expected: %s', files(1).name);
end

Lat = zeros(magiclen, nfile)

for F = 1:nfile
  thisfile = files(F).name;
  try
    f = load(thisfile);
  catch me
    %if there was a load problem, say so
    error(sprintf('Failed loading file %s', thisfile));
  end
  if any(size(f) < [magiclen,magiccol])
    error(sprintf('File %s loaded but is too small, only (%d by %d) but need (%d+ by %d+)', thisfile, size(f,1), size(f,2), magiclen, magiccol));
  end
  Lat(1:magiclen,F) = f(1:magiclen, magiccol);
end

fmt = ['\n' repmat('%15.6f', 1, nfile) '\n'];

fid = fopen(n, 'wt')
fprintf(fid, fmt, Lat.' );  %the .' is important!
fclose(fid);

Note the complete lack of a loop in writing out the data after it has all been read in.

Computing the format and using .' on the array to write out are tricks of the trade -- things that are not obvious until you have worked with MATLAB enough that suddenly they are obvious.

[joo tan]

i try run your program..same result with me..actually,what i want, extract out column from a few file and rewrite into new text file..let say, i have 10 file, so,in new text file i will have 10 column..

[Walter Roberson]

The code I show extracts out column 5 from each input file.

Please put a breakpoint in at the fprintf() line, and report back on the values of

nfile

size(Lat)

fmt

size(f)

Also, I made some changes to the code to make it more robust. (Or I will have made them in a few minutes)

[Walter Roberson]

Changes are in place.

[joo tan]

when i try run,appear error like below:

??? Undefined function or variable 'nfiles'.

Error in ==> mathwork at 24

for F = 1:nfiles

i you have time, this is a few example my file .i upload to mediafire

http://www.mediafire.com/?uabvcqlg6ksycds

[Jan]

This is a typo. If you take a short look in Walter's program, you find, that the variable is called "nfile", not "nfiles". You see, that even Walter is not a programming machine but a human. It would be nice, if you try to fix such obvious mistakes by yourself.

I had the trailing-s typo too often in my code and decided to use the singular form for *all* variables. Because "file" is not a nice name for a list of files, I use "FileList" and "nFile", or "FileC" if it matters, that the list is a CELL.

[Walter Roberson]

Sorry, yes, it was a typo, now corrected.

[Mario]

Excellent, this code fits perfectly. Thanks Walter!