What is the fastest way to determine whether a string is a number?

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Hi, I have a string x and in order to determine wether it is a number one can do the following
try
flag = isnumeric(eval(x));
catch
flag=false;
end
Is there a better and faster way to do this?
Thanks
Pat.

Accepted Answer

Sean de Wolski
Sean de Wolski on 3 Jul 2014
Edited: Sean de Wolski on 3 Jul 2014
Probably:
isnan(str2double(str))
This won't need try/catch either.
Anything with eval in it will definitely not be fast.

More Answers (1)

Cedric
Cedric on 3 Jul 2014
Edited: Cedric on 3 Jul 2014
The following should be quite fast (faster than STR2DOUBLE for example):
flag = ~isempty( sscanf( x, '%f' )) ;
EDIT: if characters can appear only at the end of the string, the following will be very fast
flag = x(end) >= '0' && x(end) <='9'
  6 Comments
Cedric
Cedric on 4 Jul 2014
Edited: Cedric on 4 Jul 2014
Can these numbers be floating point or are they integers only? Can they be negative?
Most important, do you really need to optimize further than STR2DOUBLE? The latter is certainly the most straightforward approach; most alternatives would be tricks based on some assumption(s).
For example, if you are only dealing with positive integers, the following will be quite fast
flag = all(x >= '0') && all(x <= '9') ;
Patrick Mboma
Patrick Mboma on 4 Jul 2014
Thanks Cedric, in principle, the strings can be anything: floats, negative numbers, complex, etc. The bottom line is that if a string can be evaluated to give a double, then I separate it from the rest. In that case, although str2double goes through lots of checks, it seems superior to what I did earlier

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