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

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?

[Walter Roberson]

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' ?

Answer 1

[Jan]

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);