Import and modify " .txt" files

Hi

I have some ".txt" files with this structure :

useless
useless
useless
...
data
data
...
useless
useless
useless
data
...

And I would like to have a .txt file like this :

data
data
data
...

I just know that each first line of data section begins with '1' but the length of the headerline (useless) is not fixed ! So I would like to iterate until lines begins with '1' and then keep the data.

How would you do that the easiest way ?

Thanks a lot

[Walter Roberson]

How can you tell when you have reached the end of a block of data?

What is the format of each line of the data section? Is it a single numeric value per line?

[johnmay]

Data comes from a measurement In the 'useless' section, I got the number N of measurements points (with strfind....). And N is actually the length of each data block. So I would like Matlab to delete lines until line begins with '1' then to keep lines until the end of the data block ..

Data section is a three or four columns (dépends of the data block) of numerical values

[Thorsten]

It would be best if you provide a sample file.

[johnmay]

Here is a sample file. As you can see 'X-Axis Size' gives me the number of measurement points (10) and I still have this value with some code (strfind...)

[johnmay]

Sorry, here it is... And file2 is what I want

Many thanks

Answer 1

[Thorsten]

Copy those lines that have four numbers:

fid = fopen('file.txt', 'r');
fid2 = fopen('file2.txt', 'w');

line = fgets(fid);
while line ~= -1
  [~, count] = sscanf(line, '%f');
  if count == 4
    fprintf(fid2, '%s', line);
  end
  line = fgets(fid);
end

fclose(fid)
fclose(fid2)

[johnmay]

Thanks. I have just tried...

'file2.txt' has a single line which is the first line of my data section.. :(

[johnmay]

You Genius ! Many thanks ! !

[Thorsten]

That's weird. It works smoothly for me. You could add a

 disp(line)
 disp(count)
 pause

in the loop and see if the lines are properly detected.

[johnmay]

Is it possible do this with only one file ?

[Thorsten]

You mean reading and write to the same file? No, I don't think so.

[johnmay]

Last question : when using 'fprintf' is there a way to write only the 'x' first columns of my line? and not the whole line So that the final file has a constant number of columns and could be opened easily ?

Many thanks

Answer 2

[johnmay]

Last question : when using 'fprintf' is there a way to write only the 'n' first columns of my line? and not the whole line. So that the final file has a constant number of columns (n) and could be opened easily ?

Many thanks

[Walter Roberson]

Before the loop:

   n = 2;    %whatever is appropriate

   fmt = repmat('%f ', 1, n);
   fmt(end:end+1) = '\n';    %newline, unrelated to the variable 'n'

In the loop:

[data, count] = sscanf(line, '%f');
if count >= n
  fprintf(fid2, fmt, data(1:n));
end

[johnmay]

Thanks a lot. I just tried but it doesn't work, it seems like it concatenates data in a single line.. Anyway many thanks