Creating string array using Regex.Split

Question

Alright, I'm warning you in advance, my understanding of Regular Expressions is extremely limited (I've tried my best to learn them over the years, but to be honest, I think they just frighten me.)

Let's say I have the following string:

string keyValues = "CustomerId=1||OrderId=12||UserId=a1dcd568-f129-419b-b51e-be2dbb67de0f"

This string represents key-value pairs, delimited by a user-defined string (in this case ||) (e.g. key1=value1||key2=value2). I am trying to extract the keys out of this string and store them in an array. That array would look like this:

{"CustomerId", "OrderId", "UserId"}

The best option I can think of is to use regular expressions (If someone has a better solution, please share). Here's what I'm trying to do:

string delimiter = "||";
string[] keys = Regex.Split(keyValues, "=.*" + delimiter);

I may be wrong, but the way I understand it, that regular expression is supposed to find a string that starts with = and ends with delimiter, with any number of any characters in between. Which would split the string at those positions, leaving me with the original keys, but instead, my keys array looks like this:

{"", "C", "u", "s", "t", "o", "m", "e", "r", "I", "d", "", "", ...}

As you can see, the =value|| part is stripped away. Can anyone tell me what I'm doing wrong?

EDIT

In my case, the delimiter || is a variable. I didn't mention this only because I thought I would be able to replace any references to || with delimiter. From the majority of the answers given, I now see that that is an important detail.

These two sites may be really helpful to understand Regular Expressions: google.com/support/enterprise/static/postini/docs/admin/en/… and gskinner.com/RegExr — Billy
– Billy, Commented Oct 29, 2013 at 15:48
@Billy: That Postini page only covers the POSIX ERE flavor, which is extremely limited and incompatible with .NET regexes. RegExr uses the ActionScript flavor, which is more compatible but still sorely lacking in features. This site is much more useful, and MS's own docs are pretty good. — Alan Moore
– Alan Moore, Commented Oct 29, 2013 at 16:59
@Alan Moore: You're absolutely right. I also get alot of information from the website you shared, but it's a whole load of information. I thought some explanation of the basics would be nice :) . — Billy
– Billy, Commented Oct 30, 2013 at 12:06

falsetru · Accepted Answer · 2013-10-29 16:02:55Z

3

| has special meaning in regular expression (patA|patB matches either patA or patB). Escape |.

Using non-greedy match (.*?):

string delimiter = "||";
string[] keys = Regex.Split(keyValues, @"=.*?" + Regex.Escape(delimiter));

This will give you {"CustomerId", "OrderId", "UserId=a1dcd568-f129-419b-b51e-be2dbb67de0f"}.

Matches with lookahead assertion is more appropriate:

string delimiter = "||";
string keyValues = "CustomerId=1||OrderId=12||UserId=a1dcd568-f129-419b-b51e-be2dbb67de0f";
string pattern = @"(?<=^|" + Regex.Escape(delimiter) + @")\w+(?==)";
var keys = Regex.Matches(keyValues, pattern);

BTW, use verbatim string literals (@"verbatim string literal") when express regular expression.

Demo

edited Oct 29, 2013 at 16:02

answered Oct 29, 2013 at 15:36

falsetru

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Comments

Ibrahim Najjar · Accepted Answer · 2013-10-29 15:44:39Z

2

If you just care for the keys, why not try to use a match instead of a split using:

@"[^=|]+(?==)"

If the key can't contain an equal sign = or a vertical bar |, then the above expression will match one ore more characters that are not = or | which are followed by an equal sign =, thus matching the keys.

In C#:

var input = "CustomerId=1||OrderId=12||UserId=a1dcd568-f129-419b-b51e-be2dbb67de0f";
var results = Regex.Matches(input, @"[^=|]+(?==)");

edited Oct 29, 2013 at 15:44

answered Oct 29, 2013 at 15:39

Ibrahim Najjar

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Guffa · Accepted Answer · 2013-10-29 15:55:47Z

1

An alternative is to do this without a regular expression, as the string operations are pretty basic:

string[] keys =
  keyValues.Split(new string[]{"||"}, StringSplitOptions.None)
  .Select(s => s.Substring(0, s.IndexOf('='))).ToArray();

Keep the regular expressions to the advanced string operations. :)

(When testing the performance of this solution compared to using a regular expression, this showed to be about 40 times faster.)

edited Oct 29, 2013 at 15:55

answered Oct 29, 2013 at 15:46

Guffa

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score 0 · Accepted Answer · 2013-10-29 15:52:42Z

0

Split on @"=[^|]*(?:\|\||$)"
If you need more assurance, use @"=[^=|]*(?:\|\||$)"

Edited to consume end where no delimeter exists.
Try to just use no-blank elements if its in C#.

edited Oct 29, 2013 at 15:52

answered Oct 29, 2013 at 15:44

user557597

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