Matlab textscan gone wrong: cellfun to select data from certain lines

Question

Hi I am using the following code to read some values from lines containing 'GPGGA' from data.txt

fid = fopen('D:\data.txt','r');
A=textscan(fid,'%s %*s %f %s %f %s %*s %*s %*s %*s %*s %*s %*s %*s %*s,'Delimiter',',');
fclose(fid);
Loc = [A{[2, 4]}];
row_idxs = cellfun( @(s) strcmp(s, '$GPGGA'), A{1});
Loc = Loc(row_idxs, :);
display(Loc);

The code works perfectly if the last line in data.txt is deleted. Not sure why it throws this error when the last line is included in the text file. What is the reason? I'm confused!

"??? Error using ==> horzcat CAT arguments dimensions are not consistent. Error in ==> test at 4 Loc = [A{[2, 4]}];"

data.txt

$GPGSV,4,1,16,05,15,046,23,29,47,071,21,16,31,291,18,31,39,202,18*73
$GPGSV,4,1,16,05,15,046,23,29,47,071,21,16,31,291,18,31,39,202,18*73
$GPGSV,4,1,16,05,15,046,23,29,47,071,21,16,31,291,18,31,39,202,18*73
$GPGSV,4,1,16,05,15,046,23,29,47,071,21,16,31,291,18,31,39,202,18*73
$GPGSV,4,2,16,23,13,298,17,25,15,119,17,06,22,247,16,03,04,251,14*75
$GPGSV,4,2,16,23,13,298,17,25,15,119,17,06,22,247,16,03,04,251,14*75
$GPGSV,4,2,16,23,13,298,17,25,15,119,17,06,22,247,16,03,04,251,14*75
$GPGSV,4,2,16,23,13,298,17,25,15,119,17,06,22,247,16,03,04,251,14*75

$GPGGA,1.8,98.90,S,18.0014,E,1,04,1.0,87.8,M,48.0,M,,*76
$GPGGA,1.3,98.91,S,18.0015,E,1,04,1.0,100.7,M,48.0,M,,*40
$GPGGA,1.3,98.92,S,18.0016,E,1,04,1.0,105.4,M,48.0,M,,*4F
$GPGGA,1.8,98.93,S,18.0017,E,1,04,1.0,87.8,M,48.0,M,,*76
$GPGGA,1.8,98.94,S,18.0018,E,1,04,1.0,87.8,M,48.0,M,,*76
$GPGSV,4,4,16,27,,,,26,,,,24,,,,22,,,*79

Answer 1

Your format string is no good. It is only indicative of 15 columns. The sample data you've posted has 20 columns. I suggest using the following code (which runs without error on my machine) instead:

fid = fopen('D:\data.txt','r');
A=textscan(fid,'%s %*s %f %s %f %s %*[^\n]', 'Delimiter',',');
fclose(fid);
Loc = [A{[2, 4]}];
row_idxs = cellfun( @(s) strcmp(s, '$GPGGA'), A{1});
Loc = Loc(row_idxs, :);
display(Loc);

Note the construct %*[^\n] in my format string. This tells textscan to ignore all columns from this point onwards. It is much neater than writing out lots of %*s over and over. Also, it means you're less likely to miscount the number of columns when building the format string :-)