Delete rows in a .txt table

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Dear all, i'm dealing with a problem: I have a .txt table and i want to write and delete the last n rows of this table using a condition or statement (here named solution).
here is the .txt table (shorelines.txt):
Station Profile_number shoreline_number east north distance_along_swath shoreline_elevation error analysis_type time
CLMO 5 1 681775 5955821 101.18 11.67 0.98 classic 735513.08088
CLMO 7 1 681295 5955779 197.57 50.48 4.15 classic 735513.08133
CLMO 7 2 681350 5955683 86.25 19.54 0.96 classic 735513.08154
CLMO 9 1 681116 5955539 98.12 21.44 0.67 classic 735513.08208
CLMO 9 2 681114 5955540 100.87 24.03 1.21 classic 735513.08231
CLMO 10 1 681073 5955484 82.87 19.94 0.62 stack 735513.08275
First I readed the table in this way:
%load shorelines table
while ~feof(fid)
%tline = fgetl(fid);
A=textscan(fid,'%s %u %u %f %f %f %f %f %s %f\r\n','delimiter',' ','HeaderLines',1);
for j=1:10 %number of columns (default)
data(i,j) = A(1,j);
clear j i
then I create the conditions defined as:
solution==1 %delete the last three rows of the table
solution==2 %delete the two last rows of the table
solution==3 %delete just the last row of the table
i've been trying to develop a method to delete the rows but none works. For instance, i try this:
if solution==3
tline(nim)=fgetl(nim) ;
but nothing happens... somebody have an idea how to deal with .txt tables? thanks a lot in advance...
Jules Ray
Jules Ray on 7 Oct 2013
yes, i want to read the alreay existent file.txt, but i want to edit the file removing the bottom lines (depending of the case i need to remove one, two or three lines from the lower part). I dont need to split the file. And i dont want to do any computation, just remove some lines from the lower part of the txt. Thanks.

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Accepted Answer

Cedric Wannaz
Cedric Wannaz on 7 Oct 2013
Edited: Cedric Wannaz on 7 Oct 2013
Here is a solution assuming that my comment above under your question was correct.
% - Define run parameters.
fileLocator = 'shorelines.txt' ;
headerlines = 1 ;
nList = [1,2,5,20] ;
% - Split input file name, read file.
[path_in,fname_in,ext_in] = fileparts( fileLocator ) ;
buffer = fileread( fileLocator ) ;
% - Find lines ends (must check wheter file ends with one and remove
% it from the list if present).
lineEnds = find( buffer == 10 ) ;
if buffer(end) == 10 || buffer(end-1) == 10
lineEnds(end) = [] ;
% - Loop over n's.
for k = 1 : numel( nList ) ;
% Check not case where more lines to remove than present in file.
if numel(lineEnds)-nList(k) < 1
fprintf( 'Skip removing %d lines, file contains only %d lines.\n', ...
nList(k), numel(lineEnds) ) ;
continue ;
% Compute cutoff position in buffer.
cutoff = lineEnds(end-nList(k)+1)-1 ;
% Build new file name.
fname_out = sprintf( '%s_%d.%s', fname_in, nList(k), ext_in ) ;
% Output.
fid = fopen( fullfile( path_in, fname_out ), 'w' ) ;
fwrite( fid, buffer(1:cutoff) ) ;
fclose( fid ) ;
Note that this code is just to illustrate. To make it robust, you'll have to take in account the number of header lines in the check that the number of lines to remove doesn't exceed the number of data lines, etc.
Cedric Wannaz
Cedric Wannaz on 8 Oct 2013
You're welcome.

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More Answers (1)

Walter Roberson
Walter Roberson on 7 Oct 2013
It is not possible in MATLAB to make a file shorter (except to remove everything in it) -- at least not without adding some MEX.
You should copy the parts you want to keep into another file. Afterwards you might want to rename the new file to the old.
Walter Roberson
Walter Roberson on 7 Oct 2013
Even with a .mex you would need to arrange your code so that it rewrote the entire remaining part of the file from the point that the first bit of it was deleted; and then when you got to where the new file end should be you would have the code call ftrunc() or trunc()... if you can figure out the file identifier.
None of the operating systems that MATLAB currently runs on provide a "delete line" I/O call. MATLAB file handling has always been straight sequential stream access; MATLAB was not able to use the VAX/VMS RMS (Record Management System) call for this purpose even when MATLAB ran on VMS.

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