matlab readfile with numbers - arrays

Question

In general I'm defining a matlab fnction which takes the name of a file containing some numbers, one per line, reads the data in, and then returns the data in an array.
function x = readdata(filename)
This function takes the name of a file contained in the
% character array "filename", read in the data from it, and then
% return the resulting numbers in the 1-dimensional array x. The
% array x can be n x 1 or 1 x n, where n is the number of numbers
% in the data file.
%
% If the data file cannot be found, this function should print a
% warning (using the disp() function) and return x as an empty
% array. If the data file can be found but is empty or contains
% only comments (lines starting with the Matlab comment indicator %),
% this function should return an empty array x with no warning
% message.
%
%
%I'm not sure how to check if a file exist (while they are in same folder).
%I tried if exist(filename,'file') but this is not working
This is what I have now:
function x = readdata(file)
fid = fopen(file);
tline = fgets(fid);
while isnumeric(tline)
disp(tline)
tline = fgets(fid)
Thanks

Answer 1

I would start by taking a look at the documentation that you could find here for reading in line-by-line. It even gives a sample code that you could start with:
Reading Data Line-by-Line
MATLAB provides two functions that read lines from files and store them in
string vectors: fgetl and fgets. The fgets function copies the newline
character to the output string, but fgetl does not.
The following example uses fgetl to read an entire file one line at a time.
The function litcount determines whether an input literal string (literal)
appears in each line. If it does, the function prints the entire line preceded
by the number of times the literal string appears on the line.
function y = litcount(filename, literal)
% Search for number of string matches per line.
fid = fopen(filename);
y = 0;
tline = fgetl(fid);
while ischar(tline)
matches = strfind(tline, literal);
num = length(matches);
if num > 0
y = y + num;
fprintf(1,'%d:%s\n',num,tline);
end
tline = fgetl(fid);
end
fclose(fid);
You should be able to replace what is inside the while loop with what you are looking to do.
Of note is that the fgets and fgetl functions return character arrays (strings). Thus, you'll need to first check whether the line is a comment, and then, if not, convert the string to a numeric value using something along the lines of str2double.
As for checking existence of a file, exist(filename,'file') is definitely what you want. Its documentation is found here.
You should be able to do something like:
if ~exist(filename,'file')
% Do something... I suggest the warning function, disp could be used too...
warning('The file cannot be found!')
return
end