How to split a string by delimiter from the right?

Question

How to split a string by a delimiter from the right?

e.g.

scala> "hello there how are you?".rightSplit(" ", 1)
res0: Array[java.lang.String] = Array(hello there how are, you?)

Python has a .rsplit() method which is what I'm after in Scala:

In [1]: "hello there how are you?".rsplit(" ", 1)
Out[1]: ['hello there how are', 'you?']

Answer 1

I think the simplest solution is to search for the index position and then split based on that. For example:

scala> val msg = "hello there how are you?"
msg: String = hello there how are you?

scala> msg splitAt (msg lastIndexOf ' ')
res1: (String, String) = (hello there how are," you?")

And since someone remarked on lastIndexOf returning -1, that's perfectly fine with the solution:

scala> val msg = "AstringWithoutSpaces"
msg: String = AstringWithoutSpaces

scala> msg splitAt (msg lastIndexOf ' ')
res0: (String, String) = ("",AstringWithoutSpaces)

Answer 2

You could use plain old regular expressions:

scala> val LastSpace = " (?=[^ ]+$)"
LastSpace: String = " (?=[^ ]+$)"

scala> "hello there how are you?".split(LastSpace)
res0: Array[String] = Array(hello there how are, you?)

(?=[^ ]+$) says that we'll look ahead (?=) for a group of non-space ([^ ]) characters with at least 1 character length. Finally this space followed by such sequence has to be at the end of the string: $.

This solution wont break if there is only one token:

scala> "hello".split(LastSpace)
res1: Array[String] = Array(hello)