Split a String at every 3rd comma in Java
arrays, java, split
Solution
NOTE: while solution using `split` may work (last test on Java 17) it is based on bug since look-ahead in Java should have obvious maximum length. This limitation should theoretically prevent us from using `+` but somehow `\G` at start lets us use `+` here. In the future this bug may be fixed which means that `split` will stop working.
Safer approach would be using `Matcher#find` like
String data = "0,0,1,2,4,5,3,4,6";
Pattern p = Pattern.compile("\\d+,\\d+,\\d+");//no look-ahead needed
Matcher m = p.matcher(data);
List<String> parts = new ArrayList<>();
while(m.find()){
parts.add(m.group());
}
String[] result = parts.toArray(new String[0]);
You can try to use `split` method with `(?<=\\G\\d+,\\d+,\\d+),` regex
Demo
String data = "0,0,1,2,4,5,3,4,6";
String[] array = data.split("(?<=\\G\\d+,\\d+,\\d+),"); //Magic :)
// to reveal magic see explanation below answer
for(String s : array){
System.out.println(s);
}
output:
0,0,1
2,4,5
3,4,6
Explanation
- `\\d` means one digit, same as [0-9], like `0` or `3`
- `\\d+` means one or more digits like `1` or `23`
- `\\d+,` means one or more digits with comma after it, like `1,` or `234,`
- `\\d+,\\d+,\\d+` will accept three numbers with commas between them like `12,3,456`
- `\\G` means last match, or if there is none (in case of first usage) start of the string
- `(?<=...),` is positive look-behind which will match comma `,` that has also some string described in `(?<=...)` before it
- `(?<=\\G\\d+,\\d+,\\d+),` so will try to find comma that has three numbers before it, and these numbers have aether start of the string before it (like `^0,0,1` in your example) or previously matched comma, like `2,4,5` and `3,4,6`.
Also in case you want to use other characters then digits you can also use other set of characters like
- `\\w` which will match alphabetic characters, digits and `_`
- `\\S` everything that is not white space
- `[^,]` everything that is not comma
- ... and so on. More info in Pattern documentation
By the way, this form will work with split on every 3rd, 5th, 7th, (and other odd numbers) comma, like `split("(?<=\\G\\w+,\\w+,\\w+,\\w+,\\w+),")` will split on every 5th comma.
To split on every 2nd, 4th, 6th, 8th (and rest of even numbers) comma you will need to replace `+` with `{1,maxLengthOfNumber}` like `split("(?<=\\G\\w{1,3},\\w{1,3},\\w{1,3},\\w{1,3}),")` to split on every 4th comma when numbers can have max 3 digits (0, 00, 12, 000, 123, 412, 999).
To split on every 2nd comma you can also use this regex `split("(?<!\\G\\d+),")` based on my previous answer
Problem
I have a string that looks like this: ``` 0,0,1,2,4,5,3,4,6 ``` What I want returned is a `String[]` that was split after every 3rd comma, so the result would look like this: ``` [ "0,0,1", "2,4,5", "3,4,6" ] ``` I have found similar functions but they don't split at n-th amount of commas.