Matching concatenated substrings (in any order) of two words separated by any character in C# regex

Question

Having two strings as parameters (s1, s2) I should be able to set up a new Regex(my_regular_expression(s1, s2)). For example s1="abcd", s2="xyz" I would like to match strings:

regex.IsMatched(x)==true, where x is one of the following:

abcd.xyz
abcd-xyz
xyzabcd
dxy
yzab
z a
dx
cd
but not limited to

but regex.IsMatched(y)==false, where y is one of the following:

aabcd.xyzv
abd.xyz
xycd
but not limited to

Between s1 and s2 there could be nothing or any character. Any right substring (see the function string.right(string str,int length) ) of s1 concatenated with a left substring (see the function string.left(string str,int length) ) of s2 or any right substring of s2 concatenated with a left substring of s1.

Please use s1 and s2 in regex not abcd, xyz. s1/s2 can contain special characters.

Thank you in advance.

Why would `dxy` match but not `aabcd.xyzv`? What about `xycd`? Can you update the question with a more complete definition of what the regex is supposed to match? — Ryan Gates, Mar 20 '13 at 14:17

score 1 · Accepted Answer · edited May 23 '17 at 10:25

I believe Combined would give you the expression you want. It has the following limitations.

It currently allows any character to combine the two halves (the . or - in your examples), even if it's a letter.
SuffixPart does not support Unicode characters which do not fit in a single UTF-16 code point. If you need to handle this edge case, here is a related question that talks about Java code.
For that matter PrefixPart also does not support Unicode characters which are not a single UTF-16 code point, but that method is not broken "as badly".

Here is the code:

public static string PrefixPart(string str)
{
    return
        string.Join("(?:", str.Select(i => Regex.Escape(i.ToString())))
        + string.Join(")?", Enumerable.Repeat(string.Empty, str.Length));
}

public static string SuffixPart(string str)
{
    return PrefixPart(new string(str.Reverse().ToArray()));
}

public static string Combined(string str1, string str2)
{
    string left = SuffixPart(str1) + ".?" + PrefixPart(str2);
    string right = SuffixPart(str2) + ".?" + PrefixPart(str1);
    return string.Format("^{0}|{1}$", left, right);
}

score 0 · Answer 2 · answered Mar 20 '13 at 13:53

0

I would just do

"/" + s1 + ".?" + s2 + "|" + s2 + ".?" + s1 + "/"

This would evaluate to (in your example):

/abcd.?xyz|xyz.?abcd/

That is both required patterns in either order separated by zero or one of any character.

answered Mar 20 '13 at 13:53

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This is not working for my examples: check http://derekslager.com/blog/posts/2007/09/a-better-dotnet-regular-expression-tester.ashx – algorytmus Mar 20 '13 at 14:01
@algorytmus I was able to get it to work just fine, but that site doesn't have permalinks. Here: http://rubular.com/r/qFX5Ib4Kog – Explosion Pills Mar 20 '13 at 14:15
Get rid of the `"/"` at either end. C#/.NET doesn't require you to enclose the regex in delimiters like some other flavors do. – Alan Moore Mar 20 '13 at 16:37
But "dxy" and "yzab" are not matched – algorytmus Mar 20 '13 at 16:51
@algorytmus why would you expect either of those to be matched? Maybe your rules are unclear to me – Explosion Pills Mar 20 '13 at 17:09

Matching concatenated substrings (in any order) of two words separated by any character in C# regex

2 Answers2