MATLAB: Character restriction in text file

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)

Best Answer

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'
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