Matlab ischar is not recognizing numbers

Question

I am trying to write a robust read command for my application. I want the read code to be able to handle whether the *.txt has a header (title) line or not.

The user will create a trajectory file that is always 7 columns wide and an unknown length. The first line can either be a title line for the columns or not. Typically I create my files in excel and then save them using the "Unicode Text" format. I know I could use xlsread() but I would prefer to read from a text file for versatility. Here's my current code:

In_fID=fopen([Dir,File],'r');
FirstLine=fgetl(In_fID);
model_data=textscan(In_fID,'%f %f %f %f %f %f %f');
if ischar(FirstLine)
   model_data=cell2mat(model_data);
else
   FirstLine=cell2mat(FirstLine);
    model_data=cel2mat(model_data);
   model_data=[FirstLine;model_data];
end

Regardless of whether the first line is a header line like "Time x y z r p yw" or the first coordinate of my trajectory (For example: "0 0 0 0 0 0 0") ischar(Firstline) always returns true (1). Does anyone know how I can fix this?

`ischar` checks the *datatype*, not the *content*. – Ben Voigt Oct 16 '14 at 13:13 — Ben Voigt, Oct 16 '14 at 13:13

score 2 · Answer 1 · 2014-10-16T13:21:39.190

It is normal that the result of fgetl is a char as long as you didn't reach the EOF. Type doc fgetl at MATLAB Command Window for help; you'll see that the returned value is either a text string or -1.

Now, the way the question is asked is not 100% clear what would be the expected behavior... but my guess is: you'd like to know if the first scanned line is a header or not. A good test would be to check the number of converted numeric fields returned by sscanf(FirstLine, '%f'); if is less than the expected count per line, is a big chance that is a header (it may be also a malformed line):

N_FIELDS_PER_LINE = 7;
%// . . .
if numel(sscanf(FirstLine, '%f')) ~= N_FIELDS_PER_LINE
            %// Line-Is-Header case
else
            %// Line-Is-Data case
end;

Thank you for the info on fgetl. That should have been first place I went to. — AF_Aggie, Oct 17 '14 at 01:39

score 0 · Accepted Answer · answered Oct 16 '14 at 13:24

ischar is not the best choice for the check you are trying to do.

You can do a check on the first value:

In_fID = fopen( [Dir,File] , 'r' ) ;

FirstValue =  fscanf(In_fID,'%f',1) ; %// this will return empty if the first text does not represent a number
if isempty( FirstValue )
    Headers = textscan( In_fID , '%s %s %s %s %s %s %s' , 1 ) ; %// read the header titles
else
    fseek( In_fID , 0 , 'bof' ) ; %// Rewind the cursor to the beginning of the file
end
model_data=textscan(In_fID,'%f %f %f %f %f %f %f'); %// read your data normally
fclose(In_fID) ; %// don't forget to close your file ;)

This tries to read a numeric value from the file.
If it fails (e.g. if the first text in file cannot be converted to a number), it reads a line of text header title (and move the cursor to the next line).
If the first reading return an actual value, the program rewind (replace the cursor at the beginning of the file).
The last line reads the rest of the file as numeric values.

Nice approach! I chose your answer because it is more formal and "basic enough for the next guy." I didn't realize that fscanf would return empty if the format didn't match. Thank you! — AF_Aggie, Oct 17 '14 at 01:38

Matlab ischar is not recognizing numbers

2 Answers2