Regex split string but keep separators

Question

I'd like to do a Regex.Split on some separators but I'd like to keep the separators. To give an example of what I'm trying:

"abc[s1]def[s2][s3]ghi" --> "abc", "[s1]", "def", "[s2]", "[s3]", "ghi"

The regular expression I've come up with is new Regex("\\[|\\]|\\]\\["). However, this gives me the following:

"abc[s1]def[s2][s3]ghi" --> "abc", "s1", "def", "s2", "", "s3", "ghi"

The separators have disappeared (which makes sense given my regex). Is there a way to write the regex so that the separators themselves are preserved?

Community · Accepted Answer · 2017-05-23 12:16:55Z

12

Use zero-length maching lookarounds; you want to split on

(?=\[)|(?<=\])

That is, anywhere where we assert a match of a literal [ ahead, or where we assert a match of literal ] behind.

As a C# string literal, this is

@"(?=\[)|(?<=\])"

Example in Java

    System.out.println(java.util.Arrays.toString(
        "abc[s1]def[s2][s3]ghi".split("(?=\\[)|(?<=\\])")
    ));
    // prints "[abc, [s1], def, [s2], [s3], ghi]"

    System.out.println(java.util.Arrays.toString(
        "abc;def;ghi;".split("(?<=;)")
    ));
    // prints "[abc;, def;, ghi;]"

    System.out.println(java.util.Arrays.toString(
        "OhMyGod".split("(?=(?!^)[A-Z])")
    ));
    // prints "[Oh, My, God]"

edited May 23, 2017 at 12:16

CommunityBot

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answered May 26, 2010 at 6:27

polygenelubricants

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Comments

kennytm · Accepted Answer · 2010-05-26 06:34:45Z

1

You could use .Matches instead of .Split, example (http://www.ideone.com/gUjRM):

string x = "abc[s1]def[s2][s3]ghi";
var r = new Regex(@"[^\[]+|\[[^\]]+\]");
var ms = r.Matches(x);
// do stuff with the MatchCollection `ms`.

answered May 26, 2010 at 6:34

kennytm

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