Regex to capture numeric field

Question

I am looking for a regular expression where i can extract portion of a string that meets the criteria.

string lookup "The length is 32.00 mm".

I would like to be able to get "32.00". Basically the first numeric value before " mm ". in a burte force kind of way, it can be done like this:

string test = "The length is 32.00 mm";

      int idx = test.IndexOf(" mm ") - 1;
      int endIdx = idx;
      while (idx > 0)
      {
        Char c = test.ElementAt(idx);
        if (Char.IsDigit(c) == false && c != '.')
        {
          string data = test.Substring(idx + 1, endIdx - idx + 1);
          break;
        }
        idx--;
      }

Do you have any better logic?

I can split the string by space and pick up the entry before the "mm" slot.

Thanks,

Depending on how precise it must be - even [\d.]+(?=\s+mm) might satisfy — zerkms
– zerkms, Commented Jan 8, 2015 at 4:35

Amit Joki · Accepted Answer · 2015-01-08 04:52:24Z

2

Well, you can use regex with positive lookahead

\s[\d.]+(?=\s+mm)

Like this

string test = "The length is 32.00 mm";
Console.WriteLine(Regex.Match(test, @"\s[\d.]+(?=\s+mm)").Value);

DEMO

edited Jan 8, 2015 at 4:52

answered Jan 8, 2015 at 4:35

Amit Joki

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7 Comments

Sam Over a year ago

It is close but it is matching those that don't have space between the digits and mm. "test cc 12.mm" and "test cc 12mm".

Amit Joki Over a year ago

@Sam I've changed the regex.. Take a look now

Amit Joki Over a year ago

@vks you're not seeing that I've used Regex.Match instead of Matches and the former only gives you the first match, as opposed to the latter. So your regex is a bit overkill

Amit Joki Over a year ago

@Sam also, if you want just a single space after the number and before the mm, then use [\d.]+(?= mm)

Amit Joki Over a year ago

@EhsanSajjad I would suggest going through www.regular-expressions.info

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