Regex pattern not being detected properly in C#

Question

I have a specific pattern I want to follow but the extraction process is not working as expected. I assume the pattern I developed is not correct, but I can't find the issue in it.

I have the string string test1 = "R1 0.1uF" and the pattern

"(?<des>^[a-zA-Z]+)|(?<number>\d+\s+)|(?<val>[0-9]*.?[0-9]+)|(?<units>[^,]*)";

I want it to be extracted as follows:

des: R

number: 1

val: 0.1

units: uF

Currently, des is working properly and it's finding R but the others return an empty string.

Here's my code

const string pattern = @"(?<des>^[a-zA-Z]+)|(?<number>\d+\s+)|(?<val>[0-9]*.?[0-9]+)|(?<units>[^,]*)";

string test1 = "R1 0.1uF";

Regex r = new Regex(pattern, RegexOptions.Compiled);

Match m = r.Match(test1);
string des = m.Groups["des"].Value;
string number = m.Groups["number"].Value;
string val = m.Groups["val"].Value;
string units = m.Groups["units"].Value;

Why are you joining the parts with |? That means "OR" -- it's matching the des bit, and then because that matched, it's not trying any of the other bits — canton7
– canton7, Commented Feb 19, 2020 at 15:07
You could remove the | and make it a bit more specific ^(?<des>[a-zA-Z]+)(?<number>[0-9]+)\s+(?<val>[0-9](?:\.[0-9]+)?)(?<units>[^,]*) — The fourth bird
– The fourth bird, Commented Feb 19, 2020 at 15:10
Try following : const string pattern = @"(?<des>[a-zA-Z]+)(?<number>[^\s]+)\s(?<val>[0-9]*.?[0-9]+)(?<units>.*)"; — jdweng
– jdweng, Commented Feb 19, 2020 at 15:23

Marc Lambrichs · Accepted Answer · 2020-02-19 16:32:48Z

3

Two comments:

Remove all the |s because you don't want to match des OR number OR val OR units but des followed by number followed by val followed by units
Escape the dot: \. because you want to match a dot, not some random character.

So, your regex becomes

(?<des>^[a-zA-Z]+)(?<number>\d+\s+)(?<val>[0-9]*\.?[0-9]+)(?<units>[^,]*)

Look at regex101

Some little improvements, if I may:

Move the caret ^ to the front. It doesn't belong in the first group.
Do not capture the space(s) in the group number.

Like this:

^(?<des>[a-zA-Z]+)(?:(?<number>\d+)\s+)(?<val>[0-9]*\.?[0-9]+)(?<units>[^,]*)

See regex101

edited Feb 19, 2020 at 16:32

answered Feb 19, 2020 at 15:20

Marc Lambrichs

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