Issue #9826 has been updated by Yukihiro Matsumoto.

Status changed from Feedback to Open
Assignee set to Akira Tanaka

Agreed with slice_when. Gi ahead.

Matz.


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Feature #9826: Enumerable#slice_between
https://bugs.ruby-lang.org/issues/9826#change-49004

* Author: Akira Tanaka
* Status: Open
* Priority: Normal
* Assignee: Akira Tanaka
* Category: 
* Target version: 
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I'd like to add a new method, Enumerable#slice_between.

It is similar to Enumerable#slice_before but it can use
not only the element after the slice position
but also the element before the slice position.

```
enum.slice_between(pattern_before, pattern_after=nil) -> an_enumerator
enum.slice_between {|elt_before, elt_after| bool }    -> an_enumerator
```

I found several people try to use Enumerable#slice_before for
compacting sequence of integers using hyphens:
1,2,4,9,10,11,12,15,16,19,20,21 to 1,2,4,9-12,15,16,19-21.

* ruby-talk:370132 Dave Thomas and James Edward Gray II
* http://d.hatena.ne.jp/keyesberry/20120107/p1 (in Japanese)

`slice_before` needs state management to do it.
`slice_between` can be used more easily for this situation:

```
a = [1,2,4,9,10,11,12,15,16,19,20,21]
p a.slice_between {|i, j| i+1 != j }.map {|a| a.length < 3 ? a : "#{a.first}-#{a.last}" }.join(",")
```

Or more verbosely as:

```
a = [1,2,4,9,10,11,12,15,16,19,20,21]
b = a.slice_between {|i, j| i+1 != j }
p b.to_a #=> [[1, 2], [4], [9, 10, 11, 12], [15, 16], [19, 20, 21]]
c = b.map {|a| a.length < 3 ? a : "#{a.first}-#{a.last}" }
p c #=> [[1, 2], [4], "9-12", [15, 16], "19-21"]
d = c.join(",")
p d #=> "1,2,4,9-12,15,16,19-21"
```

Also, I found several usages for Enumerable#slice_between.
* ruby-talk:359255 split logs where interval is 30s or more.
* http://stackoverflow.com/questions/6258971/how-do-i-return-a-group-of-sequential-numbers-that-might-exist-in-an-array
* ruby-talk:415057 collects same elements.  (Enumerable#chunk can be used, though.)

Any idea?


---Files--------------------------------
slice_between.patch (10 KB)
slice_between2.patch (9.7 KB)
slice_between3.patch (9.71 KB)
slice_when.patch (7.49 KB)


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