regex .net split

Question

I can split a string into two based on 2 spaces:

string Line = "1  2";

Regex.Split(Line, "  ");

=> 1, 2

I would like to add an exception. Only split if 'not enclosed by [ ]' as shown in this example.

string Line = "1  2  [1  2]";

Regex.Split(Line, "  ");

=> 1, 2, [1 2]

Can I fairly easily achieve this via regex? By the way, I use .NET.

Is it just numbers/digits? OR will it be other things like 1 2 hello [how are] you? — Eli Gassert
– Eli Gassert, Commented Nov 16, 2012 at 15:44
Intuition tells me that that's a problem beyond the scope of regex — Sam I am says Reinstate Monica
– Sam I am says Reinstate Monica, Commented Nov 16, 2012 at 15:48
And will you have nesting? 1 2 [1 2 [1 2]] 3 4 what should that produce? — Eli Gassert
– Eli Gassert, Commented Nov 16, 2012 at 15:49
There is no nesting and I only expect numbers. The answer below looks nice. — cs0815
– cs0815, Commented Nov 16, 2012 at 15:52

Martin Ender · Accepted Answer · 2012-11-16 16:12:37Z

2

You could use a lookahead, that asserts that there is no closing ] before the next opening [ or the end of the string:

Regex.Split(Line, @"[ ]+(?![^\[\]]*\])");

This will fail you if you have nested [...] structures though. Note that the lookahead is not part of the actual match, it just checks what follows without consuming anything. Inside the lookahead I used [^\[\]] which is a negated character class, matching any character except for any kind of square bracket.

Also note that this splits on 1 or more spaces. If you want to require at least two, replace [ ]+ with [ ]{2,} and if you want exactly two with [ ]{2}.

8 Comments

cs0815 Over a year ago

its does not seem to work. how does this regex look for other patterns (<> instead of [])?

Martin Ender Over a year ago

@csetzkorn it works fine for me. For input 1 2 <1 2>, use @" (?![^\<\>]*\>)". If that does not work, please let me know what exactly happens instead, and show some code if possible.

garyh Over a year ago

works for me as long as there is only one space between @" and (...

Martin Ender Over a year ago

@garyh the example input has two spaces, which is why I used two spaces in the regex (and it works for me with two spaces). I just realised that my last comment contained only one space. That was meant to be two. But maybe it's best to allow an arbitrary number: @"[ ]+(?![^\[\]]*\])" or @"[ ]+(?![^\<\>]*\>)"

cs0815 Over a year ago

Thanks it works. You forgot a space @" (?![^\<\>]*\>)" => @" (?![^\<\>]*\>)".

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