From: Glenn Jackman <glennj@...>
Date: 2010-03-23T01:45:09+09:00
Subject: Re: Grouping elements of an array

At 2010-03-20 08:57PM, "Tanaka Akira" wrote:
>  2010/3/19 Steve Wilhelm <steve@studio831.com>:
>  
> > Example (second column is timestamp in seconds starting from zero).
> >
> > A 0
> > B 15
> > C 35
> > D 100
> > E 205
> > F 215
> > G 300
> >
> > would result in
> >
> > [[A, B, C], [D], [E, F], [G]]
>  
>  I think this kind of problems which slices consecutive elements in an array
>  is not well supported in Ruby.
>  
>  Enumerable#each_slice is not usable because it slices for each fixed number
>  of elements.

I guess that's why Enumerable#each_cons exists, to iterate over a
collection and look at the next n consecutive elements.

    a = [[:A,0],[:B,15],[:C,35],[:D,100],[:E,205],[:F,215],[:G,300]]

    all = []
    current = [a[0][0]]

    a.each_cons(2) do |m, n|
      if n[1] - m[1] < 30
        current << n[0]
      else
        all << current
        current = [n[0]]
      end
    end

    all << current
    p all

>  
>  Ruby 1.9.2 has Enumerable#slice_before and it is usable but not so elegant
>  because it needs to maintain previous element.
>  
>  % ruby -e '
>  a = [
>    ["A", 0],
>    ["B", 15],
>    ["C", 35],
>    ["D", 100],
>    ["E", 205],
>    ["F", 215],
>    ["G", 300]
>  ]
>  prev = nil
>  p a.slice_before {|s,t|
>      tmp, prev = prev, t
>      tmp && (t-tmp) > 30
>    }.map {|es|
>      es.map {|s,t| s }
>    }
>  '
>  [["A", "B", "C"], ["D"], ["E", "F"], ["G"]]


-- 
Glenn Jackman
    Write a wise saying and your name will live forever. -- Anonymous