toy list processing problem: collect similar terms

[w_a_x_man]

On Sep 26, 9:24 am, p... at informatimago.com (Pascal J. Bourguignon)
wrote:
> Xah Lee <xah... at gmail.com> writes:
> > here's a interesting toy list processing problem.
>
> > I have a list of lists, where each sublist is labelled by
> > a number. I need to collect together the contents of all sublists
> > sharing
> > the same label. So if I have the list
>
> > ((0 a b) (1 c d) (2 e f) (3 g h) (1 i j) (2 k l) (4 m n) (2 o p) (4 q
> > r) (5 s t))
>
> > where the first element of each sublist is the label, I need to
> > produce:
>
> > output:
> > ((a b) (c d i j) (e f k l o p) (g h) (m n q r) (s t))
>
> > a Mathematica solution is here:
> >http://xahlee.org/UnixResource_dir/writ/notations_mma.html
>
> > R5RS Scheme lisp solution:
> >http://xahlee.org/UnixResource_dir/writ/Sourav_Mukherjee_sourav.work_...
> > by Sourav Mukherjee
>
> > also, a Common Lisp solution can be found here:
> >http://groups.google.com/group/comp.lang.lisp/browse_frm/thread/5d1de...
>
> It's too complex. Just write:
>
> (let ((list '((0 a b) (1 c d) (2 e f) (3 g h) (1 i j) (2 k l) (4 m n)
>               (2 o p) (4 q r) (5 s t))))
>
>   (mapcar (lambda (class) (reduce (function append) class :key (function rest)))
>            (com.informatimago.common-lisp.list:equivalence-classes list :key (function first)))
>
>    )
>
> --> ((S T) (Q R M N) (G H) (O P K L E F) (I J C D) (A B))
>
> --
> __Pascal Bourguignon__                    http://www.informatimago.com/

Ruby:

[[0, 'a', 'b'], [1, 'c', 'd'], [2, 'e', 'f'], [3, 'g', 'h'], [1,
'i', 'j'], [2, 'k', 'l'], [4, 'm', 'n'], [2, 'o', 'p'], [4, 'q', 'r'],
[5, 's', 't']].
group_by{|x| x.first}.values.map{|x| x.map{|y| y[1..-1]}.flatten}

    ==>[["s", "t"], ["a", "b"], ["c", "d", "i", "j"],
 ["e", "f", "k", "l", "o", "p"],
 ["g", "h"], ["m", "n", "q", "r"]]