CODEWITHSUNDEEP
c#regex
Jeffrey
Jeffrey

Reputation: 538

Regex Grouping returns no values

I'm trying to get some named groups(X, Y, Z, W, P, R) from a string and I'm having problems getting the output.

This is the part of the string that has the info I am trying to extract:

[1,1] = Group: 1   Config:
X:  -196.999   Y:   1009.999   Z:  210.342
W:  90   P:   0   R:  90

I tried to get the values using the following

@"(?<X>(?<=X:\s*)([+-]?\d*(\.\d+)?))
  (?<Y>(?<=Y:\s*)([+-]?\d*(\.\d+)?))
  (?<Z>(?<=Z:\s*)([+-]?\d*(\.\d+)?))
  (?<W>(?<=W:\s*)([+-]?\d*(\.\d+)?))
  (?<P>(?<=P:\s*)([+-]?\d*(\.\d+)?))
  (?<R>(?<=R:\s*)([+-]?\d*(\.\d+)?))"

but I didn't get any values.

Only when I use @"(?<X>(?<=X:\s*)([+-]?\d*(\.\d+)?)(?=\s*Y:))" do I get the correct value for the X Group.

However this

@"(?<X>(?<=X:\s*)([+-]?\d*(\.\d+)?)(?=\s*Y:))
  (?<Y>(?<=Y:\s*)([+-]?\d*(\.\d+)?)(?=\s*Z:))"

Also doesn't give me any values.

Eventually matching Config:\s* will also come into play and when I try this

@"(?<=Config:\s*)(?<X>(?<=X:\s*)([+-]?\d*(\.\d+)?)(?=\s*Y:))"

I don't get a value, but this does

@"(?<=:\s*)(?<X>(?<=X:\s*)([+-]?\d*(\.\d+)?)(?=\s*Y:))"

So, A) I don't understand why I need the lookahead (?=\s*Y:) to get the value

B) Why does it fail if I add another group?

C) Why am I not matching Config?

Could someone explain to me what I'm doing wrong here?

Upvotes: 2

Views: 53

Answers (1)

Tim Biegeleisen
Tim Biegeleisen

Reputation: 520908

I suggest a different approach where you just try to find each letter label and its associated float value:

string input = "[1,1] = Group: 1   Config:\nX:  -196.999   Y:   1009.999  \nZ:  210.342\nW:  90   P:   0   R:  90";
var re = new Regex(@"\b([A-Z]+):\s*([+-]?\d+(?:\.\d+)?)\b");
MatchCollection matches = re.Matches(input);
for (int mnum = 0; mnum < matches.Count; mnum++)
{
    Match match = matches[mnum];
    Console.WriteLine("{0}: {1}", match.Groups[1], match.Groups[2]);
}

This prints:

X: -196.999
Y: 1009.999
Z: 210.342
W: 90
P: 0
R: 90

This approach completely avoids the problem of using named capture groups, and instead just tries to match and capture a letters label, followed by a floating point number.

Upvotes: 3

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