Feature #9116

String#rsplit missing

Added by Ramkumar Ramachandra over 1 year ago. Updated over 1 year ago.

[ruby-core:58375]
Status:Open
Priority:Normal
Assignee:-

Description

There's nothing corresponding to Python's rsplit(). A quick glance at rb_str_split_m() tells me that it should be pretty trivial to implement. Is there any specific reason it hasn't already been done?

History

#1 Updated by Matthew Kerwin over 1 year ago

On Nov 16, 2013 6:35 PM, "artagnon (Ramkumar Ramachandra)" <
artagnon@gmail.com> wrote:

There's nothing corresponding to Python's rsplit(). A quick glance at
rb_str_split_m() tells me that it should be pretty trivial to implement. Is
there any specific reason it hasn't already been done?

What is rsplit? How does it differ from split (with or without a second
paramater)? What is the use-case/demand for it?

Sent from my phone, so excuse the typos.

#2 Updated by Alexey Muranov over 1 year ago

Out of curiosity, i have looked it up: http://docs.python.org/3/library/stdtypes.html#str.rsplit

#3 Updated by Robert A. Heiler over 1 year ago

I am still not sure how it differs from #split().

#4 Updated by Robert A. Heiler over 1 year ago

Oh, now I see:

"Except for splitting from the right, rsplit() behaves like split() which is described in detail below."

So it basically splits from the right, not left, unlike #split() which splits from the left, I think.

I suppose in Ruby you can do .reverse.split, but perhaps rsplit may be more convenient. (I myself don't think I have had a need to use something similar to rsplit so far).

#5 Updated by Matthew Kerwin over 1 year ago

=begin
I, too, looked up and read the documentation, a couple of times.

I understand that the difference only applies when a ((|limit|)) parameter is given, and so examples of the new API would be:

'a.b.c'.rsplit('.') #=> ["a", "b", "c"], same as #split
'a.b.c'.rpslit('.', 2) #=> ["a.b", "c"]

I would want to clarify some of the other edge cases (from ((%String#split%))) before continuing:

  • If ((|pattern|)) is a (({String})), then its contents are used as the delimiter when splitting ((%str%)). If ((|pattern|)) is a single space, ((|str|)) is split on whitespace, with leading whitespace and runs of contiguous whitespace characters ignored.

Would this have some right-handed equivalent in ((%#rsplit%))? E.g. "...with trailing whitespace and runs..."? Or would it remain the same as ((%#split%))? Or some third option?

E.g.:
' x y '.rsplit(' ') #=> ["x", "y"], same as split?
' x y '.split(' ',-1) #=> ["", "x", "y"] or ["x", "y", ""] or ..?

  • If the ((|limit|)) parameter is omitted, trailing null fields are suppressed. If ((|limit|)) is a positive number, at most that number of fields will be returned (if ((|limit|)) is (({1})), the entire string is returned as the only entry in an array). If negative, there is no limit to the number of fields returned, and trailing null fields are not suppressed.

Similarly, would this become: "...leading null fields..." in both instances?

E.g.:
'..x..'.rsplit('.') #=> ["x", "", ""] or ["", "", "x"] or ..?
'..x..'.rsplit('.',-1) #=> ["", "", "x", "", ""], same as #split?

Note that this would be another difference from ((%#split%)), which ((*doesn't*)) depend on the ((|limit|)) parameter.

Seems like a lot of work. What is the demand for this feature?
=end

#6 Updated by Alexey Muranov over 1 year ago

=begin
--- phluid61 (Matthew Kerwin) wrote:

--- > I understand that the difference only applies when a ((|limit|)) parameter is given

It is not only when (({limit})) parameter is given:

"aaa".split("aa") # => ["", "a"]
"aaa".rsplit("aa") # => ["a", ""]

Maybe with a regex there can be a more meaningful example.
=end

#7 Updated by Alexey Muranov over 1 year ago

=begin
--- phluid61 (Matthew Kerwin) wrote:

--- > Would this have some right-handed equivalent in ((%#rsplit%))? E.g. "...with trailing whitespace and runs..."? Or would it remain the same as ((%#split%))? Or some third option?

IMO, if it is introduced, i would say it must be completely symmetric with (({split})).
=end

#8 Updated by Matthew Kerwin over 1 year ago

=begin
alexeymuranov (Alexey Muranov) wrote:

It is not only when (({limit})) parameter is given:

"aaa".split("aa") # => ["", "a"]
"aaa".rsplit("aa") # => ["a", ""]

Ah, I see. Thank you.

Maybe with a regex there can be a more meaningful example.

I'm interested to see how it would be achieved with regex, from an implementation point of view.

=end

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