Split regex to extract Strings of contiguous characters

Question

Is there a regex that would work with String.split() to break a String into contiguous characters - ie split where the next character is different to the previous character?

Here's the test case:

String regex = "your answer here";
String[] parts = "aaabbcddeee".split(regex);
System.out.println(Arrays.toString(parts));

Expected output:

[aaa, bb, c, dd, eee]

Although the test case has letters only as input, this is for clarity only; input characters may be any character.

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Please do not provide "work-arounds" involving loops or other techniques.

The question is to find the right regex for the code as shown above - ie only using split() and no other methods calls. It is not a question about finding code that will "do the job".

Christychristye

Answer 1

It is totally possible to write the regex for splitting in one step:

"(?<=(.))(?!\\1)"

Since you want to split between every group of same characters, we just need to look for the boundary between 2 groups. I achieve this by using a positive look-behind just to grab the previous character, and use a negative look-ahead and back-reference to check that the next character is not the same character.

As you can see, the regex is zero-width (only 2 look around assertions). No character is consumed by the regex.

Manchu

in .net character within the group i.e (.) is also included in the result..i wonder why it's not the case with java – Scholarship

@Some1.Kill.The.DJ: I guess there are some difference here and there between different languages. I have no idea to how achieve the same effect in .NET (or Ruby, since it also include capturing group in the result of split). – Manchu