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

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Patrick Mboma 2014-7-3

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评论： Patrick Mboma 2014-7-4

采纳的回答： Sean de Wolski

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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.

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Sean de Wolski 2014-7-3

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编辑：Sean de Wolski 2014-7-3

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Probably:

isnan(str2double(str))

This won't need try/catch either.

Anything with eval in it will definitely not be fast.

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Patrick Mboma 2014-7-3

Hi Sean, Your solution does work and is superior to mine.

thanks,

Pat.

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Cedric 2014-7-3

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编辑：Cedric 2014-7-3

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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'

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Cedric 2014-7-4

编辑：Cedric 2014-7-4

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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 2014-7-4

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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