I need to read and rewrite only certain lines of a text file.

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Joseph
Joseph on 20 Jun 2013
I have a text file full of data. The file has multiple data sets, often more that 100. I only need the last 2 data points in each set however. So for example I currently have:
Data 1
C 2 3 5
C 2 3 7
C 2 2 9
C 3 10 -7
Data 2
C 2 8 9
C -9 -3 7
C 4 -2 14
C 0 0 0
And I need to write a text file that reads.
2 2 9
3 10 -7
4 -2 14
0 0 0
I currently have code that removes the first data label, the first two lines of the data, and the side "C" labels but I am unsure how get this to loop for the rest of the data. My code is as follows.
fid = fopen('Test_Data_2.txt', 'rt');
datacell = textscan(fid, '%*s %f %f %f', 'HeaderLines', 3, 'CollectOutput', 1);
fclose(fid);
datacell{1};
dlmwrite('md_msd.out', datacell{1}, 'delimiter', '\t', ...
'precision', 6)
I just need to get rid of any unwanted data after the first data set. Can anybody help me?
  1 Comment
Walter Roberson
Walter Roberson on 20 Jun 2013
Are there a fixed number of lines for each dataset? Do the lines that mark the beginning of the next dataset always start with 'Data' ?

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Accepted Answer

Jan
Jan on 20 Jun 2013
Str = fileread('Test_Data_2.txt');
CStr = regexp(Str, '\n', 'split');
Match = strcnmp(CStr, 'Data', 4);
Index = find(Index);
Match(Index + 1) = true;
Match(Index + 2) = true;
CStr(Match) = []; % Remove the 'Data x' and the two following lines
CStr = strrep(CStr, 'C ', ''); % Remove leading 'C '
FID = fopen('Test_Data_2_out.txt', 'w');
if FID == -1, error('Cannot open file for writing'); end
fprintf(FID, '%s\n', CStr{:});
fclose(FID);

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