How to remove lines that do not start with specific characters?

The file consists of values like

v 1 2 3

v 1 2 3

vt 1 2 3

vn 1 2 3

f 1 2 3

I want only lines that start with v or f -- other lines should be removed .

How to do this? Please help me. Thanks in advance.

Is it possible using this regexprep?

[Sharen H]

any simple statements to do this

Answer 1

[Sriram]

try using

 strncmp %%function

http://www.mathworks.in/help/matlab/ref/strncmp.html

Answer 2

[Walter Roberson]

infile = fileread('YourFileName.txt');

newfile = regexprep(infile, '^[^vf].*$', '', 'lineanchors', 'dotexceptnewline');

fid = fopen('NewFileName.txt');
fwrite(fid, newfile);
fclose(fid)

[Sharen H]

its not working..

the output which i expect is

v 1 2 3

v 1 2 3

f 1 2 3

can u please explain what it does

[Walter Roberson]

All the lines you show in your sample begin with either 'v' or 'f'. A line that starts with 'vn' still starts with 'v'.

What you probably want is

infile = fileread('YourFileName.txt');

newfile = regexp(infile, '^[vf]\s.*$', 'match', 'lineanchors', 'dotexceptnewline')

fid = fopen('NewFileName.txt', 'wt');
fprintf(fid, '%s\n', newfile{:});
fclose(fid);

YourFileName.txt and NewFileName.txt should be replaced by the actual input file name, and the actual name of the new file you want.

The regexp expression here means to look for input lines in the string "infile" that start with the letter v or f, followed by whitespace, and then anything until the end of the line, and copy those lines to the cell array of strings "newfile".

[Jan]

@Sharen: Please do not post "not working" without any explanations in the forum. Do you get an error message (which one?) or do the results differ from your expectations (how?)?