Character restriction in text file

I am trying to restrict a text file by only keeping lines that contain 'M' in the first column.

I wrote the code below, except 'M' cannot be used in str2double. Would there be an alternative way to write this? Code below:

clear all
fidi = fopen('BTM.txt','rt');
Glxc  = textscan(fidi, '%s', 'Delimiter','|');
frewind(fidi)
Glxcs = textscan(fidi, '%s', 'EndOfLine','\r\n');
fclose(fidi);
dlen = 2*fix(length(Glxc{:})/2);                          % Set Row Length
Glxcr = reshape(Glxc{:}(1:dlen), 2, [])';                  % Reshape & Transpose
LIdx= (str2double(Glxcr(:,2))<=1813.1) & (str2double(Glxcr(:,1))='M')% Reshape & Transpose
NewGlxc = Glxcs{:}(LIdx,:);                                 % Rows Of New Array
fido = fopen('vcc18M.txt','wt')
fprintf(fido, '%s\n', NewGlxc{:});
fclose(fido)

[Star Strider]

‘... pulling lines that contain 'M' in the first column ...’

Does that mean that you want to keep those lines or discard them?

[jgillis16]

keep those lines, discard the rest that don't have 'M' in the first column.

Answer 1

[Walter Roberson]

LIdx = (str2double(Glxcr(:,2))<=1813.1) & ~cellfun(@isempty, regexp(Glxcr(:,1),'^M$'))

If the column only needs to start with 'M' but can contain other characters, use '^M' . If the column only needs to have 'M' somewhere in it, use 'M'

Answer 2

[Cedric]

If you want to keep only the lines which start with the character M, the following would work:

 content = fileread( 'BTM.txt' ) ;
 content = regexprep( content, '^[^M].*?$\s*', '', 'lineanchors' ) ;

And then you export keeping the original format:

 fId = fopen( 'vcc18M.txt', 'w' ) ;
 fwrite( fId, content ) ;
 fclose( fId ) ;

PS: Will you ultimately want to separate lines like here? Were you able to make this one work by the way?

EDIT : Without knowing more about the content of the file, it is difficult to debug what you wrote, but if Glxcr(:,1) is truly indexing cells which contain elements of the first column of the file, then you probably want to replace

 & (str2double(Glxcr(:,1))='M')

with

 & strcmp( Glxcr(:,1), 'M' )