Help writing a regular expression

Question

I asked a very similar question to this one almost a month ago here.

I am trying very hard to understand regular expressions, but not a bit of it makes any sense. SLak's solution in that question worked well, but when I try to use the Regex Helper at http://gskinner.com/RegExr/ it only matches the first comma of -2.2,1.1-6.9,2.3-12.8,2.3 when given the regex ,|(?<!^|,)(?=-)

In other words I can't find a single regex tool that will even help me understand it. Well, enough whining. I'm now trying to re-write this regex so that I can do a Regex.Split() to split up the string 2.2 1.1-6.9,2.3-12.8 2.3 into -2.2, 1.1, -6.9, 2.3, -12.8, and 2.3.

The difference the aforementioned question is that there can now be leading and/or trailing whitespace, and that whitespace can act as a delimiter as can a comma.

I tried using \s|,|(?<!^|,)(?=-) but this doesn't work. I tried using this to split 293.46701,72.238185, but C# just tells me "the input string was not in a correct format". Please note that there is leading and trailing whitespace that SO does not display correctly.

EDIT: Here is the code which is executed, and the variables and values after execution of the code. enter image description here

Can you post your code (not just the regular expression, but also the way you are using it) and show which line gives the error. — Mark Byers, Mar 20 '11 at 20:31
@Mark - Done. You can see that it is not splitting correctly. — Adam S, Mar 20 '11 at 20:42
Will there ever be floats in scientific notation? (possibly having exponents having optional sign?) i.e. `+1.2E-23` — ridgerunner, Mar 21 '11 at 02:22

score 5 · Answer 1 · answered Mar 20 '11 at 20:45

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If it doesn't have to be Regex, and if it doesn't have to be slow :-) this should do it for you:

var components = "2.2 1.1-6.9,2.3-12.8 2.3".Replace("-", ",-").
Split(new[]{' ', ','},StringSplitOptions.RemoveEmptyEntries);

Components would then contain:[2.2 1.1 -6.9 2.3 -12.8 2.3]

answered Mar 20 '11 at 20:45

rasmusvhansen

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+1 seems like a great solution for someone that is having a hard time with regular expressions. – juharr Mar 20 '11 at 22:02

Andy Edinborough · Answer 2 · 2011-03-20T20:39:32.393

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Does it need to be split? You could do Regex.Matches(text, @"\-?[\d]+(\.[\d]+)?").

If you need split, Regex.Split(text, @"[^\d.-]+|(?=-)") should work also.

P.S. I used Regex Hero to test on the fly http://regexhero.net

edited Mar 20 '11 at 20:39

answered Mar 20 '11 at 20:33

Andy Edinborough

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Or you could use Regex.Split(",")... or for that matter String.Split(","). – harpo Mar 20 '11 at 20:36
It makes no difference for the results, but consider using `?` instead of `{0,1}`. – jb. Mar 20 '11 at 20:38
I like `{0,1}` because it looks more complicated. :]] j/k, you're right. I've edited the answer. – Andy Edinborough Mar 20 '11 at 20:41
Actually, Matches works perfectly! Now I just have to figure out how to extract those matches into an array of doubles. – Adam S Mar 20 '11 at 20:52
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Pretty simple with Linq: `Regex.Matches(text, @"\-?[\d]+(\.[\d]+)?").Cast().Select(x=>Convert.ToDouble(x.Value)).ToArray()` – Andy Edinborough Mar 20 '11 at 21:02

Town · Answer 3 · 2011-03-20T21:57:02.123

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Unless I'm missing the point entirely (it's Sunday night and I'm tired ;) ) I think you need to concentrate more on matching the things you do want and not the things you don't want.

Regex argsep = new Regex(@"\-?[0-9]+\.?[0-9]*");
string text_to_split = "-2.2 1.1-6.9,2.3-12.8 2.3 293.46701,72.238185";
var tmp3 = argsep.Matches(text_to_split);

This gives you a MatchCollection of each of the values you wanted.

To break that down and try and give you an understanding of what it's saying, split it up into parts:

\-? Matches a literal minus sign (\ denotes literal characters) zero or one time (?)
[0-9]+ Matches any character from 0 to 9, one or more times (+)
\.? Matches a literal full stop, zero or one time (?)
[0-9]* Matches any character from 0 to 9 again, but this time it's zero or more times (*)

You don't need to worry about things like \s (spaces) for this regex, as the things you're actually trying to match are the positive/negative numbers.

edited Mar 20 '11 at 21:57

answered Mar 20 '11 at 21:04

Town

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If you look at the very first string in the OP's question, it does say `-2.2`, he must have copied it wrong the second time. – jb. Mar 20 '11 at 21:14
Ah yes, so it does! It definitely *is* Sunday night and I definitely *am* tired ;) Regex still works regardless though, so not all bad :) – Town Mar 20 '11 at 21:17
Yep yep, no worries. If I were to use regex to solve this it would look pretty darn close to yours. – jb. Mar 20 '11 at 21:18
It has a couple of minor problems. `4711.` is matched as a number and `.4711` is matched as `4711`. – Jonas Elfström Mar 20 '11 at 21:34
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http://stackoverflow.com/questions/4246077/simple-problem-with-regular-expression-only-digits-and-commas/4247184#4247184 makes me think that it's probably better to split than to try to match numbers. – Jonas Elfström Mar 20 '11 at 21:40
Haha! Good point, well made. That reference is a pedant's delight! It could be argued that 4711. should be matched as a number (double.Parse() will parse it as 4711.0). .4711 shouldn't be matched as 4711 though, which is the case for Andy's one too. The OP gave a few examples and both regexes match the provided examples though. – Town Mar 20 '11 at 21:50

score 0 · Answer 4 · answered Mar 20 '11 at 20:34

0

Consider using the string split function. String operations are way faster than regular expressions and much simpler to use/understand.

answered Mar 20 '11 at 20:34

Zebi

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Take a look at rasmusvhansens answer :) – Zebi Mar 20 '11 at 21:34

score 0 · Answer 5 · answered Mar 20 '11 at 20:44

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If the "Matches" approach doesnt work you could perhaps hack something in two steps?

Regex RE = new Regex(@"(-?[\d.]+)|,|\s+");
RE.Split(" -2.2,1.1-6.9,2.3-12.8,2.3 ")
       .Where(s=>!string.IsNullOrEmpty(s))

Outputs:

-2.2
1.1
-6.9
2.3
-12.8
2.3

answered Mar 20 '11 at 20:44

svrist

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Help writing a regular expression

5 Answers5