How to extract rows from a text file with a specific start?

Question

Michael Lim 2017-2-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/327318-how-to-extract-rows-from-a-text-file-with-a-specific-start

评论： Andreas Voldstad 2020-2-22

$GNRMC,083059.00,A,2948.16655,N,12133.72003,E,0.018,,280217,,,D*69
$GNVTG,,T,,M,0.018,N,0.034,K,D*36
$GNGGA,083059.00,2948.16655,N,12133.72003,E,4,12,0.90,5.0,M,10.9,M,1.0,0790*64
$GNGSA,A,3,23,27,16,14,26,31,,,,,,,2.00,0.90,1.78*19
$GNGSA,A,3,80,73,82,83,70,81,71,,,,,,2.00,0.90,1.78*1C

For example I have this kind of text file (it continues on for very long) and I want to extract only the rows starting with $GNGGA and write them all to another text file

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Answer 1

Jan 2017-2-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/327318-how-to-extract-rows-from-a-text-file-with-a-specific-start#answer_256672

编辑：Jan 2017-2-28

在 MATLAB Online 中打开

% Parameter:
FileName = 'C:\Your data file.txt';
Key      = '$GNGGA';
NewFile  = 'C:\Fixed.txt';
% Import text file and select lines starting with the Key string:
Str   = fileread(FileName);
CStr  = strsplit(Str, '\n');
Match = strncmp(CStr, Key, length(Key));
CStr  = CStr(Match);
% Create new file and write matching lines:
fid = fopen(NewFile, 'w');
if fid == -1
  error('Cannot create new file: %s', NewFile);
end
fprintf(fid, '%s\n', CStr{:});
fclose(fid);

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dpb 2018-10-25

编辑：dpb 2018-10-25

在 MATLAB Online 中打开

Keep or remove? Following removes; reverse sense of contains logic test to keep--

keys=cellstr(['X':'Z'].');
fid1=fopen('yourfile');
fid2=fopen('newfile','w');
while ~feof(fid)
  l=fgets(fid);
  if contains(l(1),keys); continue, end  % not found, go on
  fwrite(fid2,l)                         % found, write 
end
fid1=fclose(fid1);
fid2=fclose(fid2);

Andreas Voldstad 2020-2-22

Hi!

I have a very similar problem, trying to find lines in a txt file starting with 'TuneOnset', which also contains onset times at the end of the line in milliseconds.

I tried this solution as a start, but somehow I can't get it to work.

The code works and I get no errors, the file is split up into cells based on lines in the text, and the cells look like I expect, some of them starting with 'TuneOnset', but strncmp does not match it and outputs only logical 0s.

Does any one have any idea why this would not work for me, or an alternative solution for extracting a number at the end of lines starting with some specific string?

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Answer 2

dpb 2017-2-28

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/327318-how-to-extract-rows-from-a-text-file-with-a-specific-start#answer_256674

编辑：dpb 2017-3-1

在 MATLAB Online 中打开

"Dead-ahead" solution...

fid1=fopen('yourfile');
fid2=fopen('newfile','w');
while ~feof(fid)
  l=fgets(fid);
  if isempty(strfind(l,'$GNGGA')), continue, end  % not found, go on
  fwrite(fid2,l)                         % found, write 
end
fid1=fclose(fid1);
fid2=fclose(fid2);

Alternatively, read full file into memory and do the search there if not too big...

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Satya Gopal 2019-11-19

Hi, I've been trying to do the same thing. Your code works well. I just had a problem with it. If I have items like alpha, alpha/all, beta, beta/all in the first row and i put the strfind input for 'alpha', it copies alpha and alpha/all rows as well. Can anyone help with extract string match?

dpb 2019-11-19

strcmp and strncmp are exact matches...you have to define a unique string as the pattern that allows you to segregate as desired. With multiple patterns, depending upon what you're actually trying to accomplish you may need to do a second compare for the 'all' pattern having found the record containing the other key word.

Or, switch to using regular expressions for more general pattern matching.

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