Benchmarking IsNumeric Options
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by J. Ambrose Little
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Conclusions

So which method should you use?  It depends on the application, and maybe on your choice of language.  With regard to the latter, I simply concede that if you are using the VB.NET IDE, it is very easy to just use IsNumeric, and since it is fast and flexible, it may be the option of choice in that environment.  But even if you are using the VB.NET IDE, you may want to consider using Double.TryParse.

In any case, keep in mind that for the given regular expression and incremental char comparison implementations, the definition of "IsNumeric" is limited to digits with one optional decimal.  If you needed to expand this definition to include, e.g., allowing globalization, allowing signs, allowing scientific notation, etc., you could customize them to meet your definition of what a number is, but I would expect that as you get more flexible with the definition, these methods would start to lose out in raw performance (and simplicity).

Therefore, given the insignificant practical performance difference between the Incremental Char, Double.TryParse, and VisualBasic IsNumeric methods, I would choose either Double.TryParse or VB IsNumeric since their definitions of "IsNumeric" include many common variations not accounted for in the Regular Expression or Incremental Char.  Clearly, using one of the Try-Catch methods is a bad idea due to the terrible performance for bad inputs; only use these if you truly do need to handle the exception. 

For most applications, the best method will be TryParse because it offers the most flexibility in definition, the ability to return the converted value concurrently with the type check, and it is part of the System library, so no extra references or work is needed to use it, no matter what language you choose.  If you find it too cumbersome to use directly (because it offers no overloads), you can always wrap it in a static IsNumeric method that only requires the input to check as a parameter.


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Title: Straight to the point   
Name: Fabio C. Rispoli
Date: 2006-08-01 4:16:33 PM
Comment:
Congratulations for the article. Simple and straight to the point.

Thanks.
Title: Mr.   
Name: mike
Date: 2006-04-05 10:30:42 AM
Comment:
double.TryParse is also slower than Incremental Chars.
Title: Gopal   
Name: Ambrose
Date: 2006-03-22 1:19:05 PM
Comment:
Gopal,

It's been a long time that I looked at this, but I seem to recall that the VB code didn't use double.TryParse. Maybe it was updated? Are you looking at v2 because this was written before v2 was in alpha...
Title: Another note   
Name: gopal
Date: 2006-03-22 1:13:08 PM
Comment:
Incremental char returns true for empty strings.
Also, looking at the disassembly code, Visualbasic Isnumeric uses Double.TryParse.
Title: just a note   
Name: E
Date: 2006-02-16 3:37:19 PM
Comment:
I was just noticing that the Incremental Char method returns false for negative numbers. . .
Title: IsNumeric?   
Name: Peter Hartlén
Date: 2005-11-17 3:31:17 AM
Comment:
First of all, I did the test with converting a string to integer. Although the code needed for this was a bit more than I at first expected, the performance overhead (compared to simple TryParse) was not that much. The code I used:

public bool TryParseToInt ( string expression, out int iIntVal )
{
double dVal;
bool bRes;

bRes = double.TryParse(expression,
NumberStyles.Integer,
NumberFormatInfo.CurrentInfo,
out dVal);

if( dVal > Int32.MaxValue || dVal < Int32.MinValue )
{
iIntVal = 0;
bRes = false;
}
else
iIntVal = Convert.ToInt32(dVal);

return bRes;
}

As you can see, this method both tests if the string is a valid integer (Int32), and if so, converts the value using the out parameter.

Regarding your results (compared to mine):

Are you sure the data for VB's IsNumeric is correct? During my tests it shows the same performance as try-catch blocks. I’ve read that IsNumeric uses try/catch itself, so it’s merely a wrapper.

The execution time for the Regular Expression method increases quite dramatically when I increase the length of the input string and the faulty character is at the end.

Also worth mention, I did a test with 1 million strings where 2% where faulty (i.e. non-numbers). The performance between a try-catch block function and a TryParse-based function was negligible. So in the real life (where you won’t find 100% correct nor 100% erroneous data), the result looks quite different!
Title: Have to be careful   
Name: Steve Maier
Date: 2005-11-16 11:38:30 AM
Comment:
One thing to remember tho with the incremental character approach is localization. some places use ',' for the decimal point and '.' for the grouping character. With the Parse and TryParse methods, they can take the culture value and will parse things correctly.
Title: Nice reading!   
Name: Peter Hartlén
Date: 2005-11-16 10:16:27 AM
Comment:
Thanks, this was exactly what I was looking for!

I'm using Compact Framework and for example Int32.TryParse is not available, it would be interesting to see the performance of Double.TryParse (using NumberFormat.Integer), with a cast to Int32. I will try this using your code!

Thanks again!
Title: Thanks for the article !   
Name: Deon
Date: 2005-11-02 8:43:18 AM
Comment:
Great article.

Thanks for the effort
Title: Ms.   
Name: Ututu
Date: 2005-08-09 12:32:04 PM
Comment:
Very good article, thanks a lot.
Title: Try-Catch   
Name: J. Ambrose Little
Date: 2005-07-20 8:13:44 AM
Comment:
Try-catch statements are integral to a good program, but they should only be used where they need to be used. There are some good topics on Exception Management in the MSDN Library that you should review to better understand.
Title: Mr.   
Name: Ram Kinkar Pandey
Date: 2005-07-20 5:24:46 AM
Comment:
I was just Looking why using try..catch in ASP.NET is bad idea. This article makes this very clear to me.
Thank you
Title: Mr.   
Name: Linanga Keeba
Date: 2005-07-18 2:23:36 PM
Comment:
The article assisted me very much. Thanks.






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