Asp Forum - Ruby for arranging fencing competitions

Milo Thurston

10/16/2007 2:31:00 PM

Sport fencing competitions are organised in pools, where every fencer
fences every other and the total score is totted up at the end. Sheets
like this are used to keep track of which bouts have been played and
what the score is:
http://www.soton.ac.uk/~fencing/file...
These sheets show an order of bouts for between 4-7 fencers, a typical
number in a pool. An impending competition* got me wondering how one
might use Ruby to generate those lists of bouts. A simple list of what
bouts need to be fought is easy, and I wrote a simple script that
produces an array of the following values for any number of contestants
(in this case 4):

1 - 2
1 - 3
1 - 4
2 - 3
2 - 4
3 - 4

The difficult bit is that fencers need to be given a rest between bouts
if possible, so this order won't do. Simply randomising this array may
still mean someone having to do more than one fight in a row. Not having
a mathematical background I can't think of a suitable method to approach
this, and if anyone could suggest some hints I'd be interested to know.

* I can, of course, use the existing pool sheets for the competition;
this is just for my amusement.
--
Posted via http://www.ruby-....

5 Answers

Jesús Gabriel y Galán

10/16/2007 2:43:00 PM

Milo Thurston

10/16/2007 2:50:00 PM

JesÃºs Gabriel y GalÃ¡n wrote:
> Food for RubyQuiz?

Thanks - I'll take a look.

--
Posted via http://www.ruby-....

Rick DeNatale

10/16/2007 6:22:00 PM

On 10/16/07, Milo Thurston <knirirr@gmail.com> wrote:
> Sport fencing competitions are organised in pools, where every fencer
> fences every other and the total score is totted up at the end. Sheets
> like this are used to keep track of which bouts have been played and
> what the score is:
> http://www.soton.ac.uk/~fencing/file...
> These sheets show an order of bouts for between 4-7 fencers, a typical
> number in a pool. An impending competition* got me wondering how one
> might use Ruby to generate those lists of bouts. A simple list of what
> bouts need to be fought is easy, and I wrote a simple script that
> produces an array of the following values for any number of contestants
> (in this case 4):
>
> 1 - 2
> 1 - 3
> 1 - 4
> 2 - 3
> 2 - 4
> 3 - 4
>
> The difficult bit is that fencers need to be given a rest between bouts
> if possible, so this order won't do. Simply randomising this array may
> still mean someone having to do more than one fight in a row. Not having
> a mathematical background I can't think of a suitable method to approach
> this, and if anyone could suggest some hints I'd be interested to know.

How about:

class RoundRobinPairsGenerator

attr_reader :competitors, :full_size

def initialize(n)
@competitors = (1..n).to_a
@full_size = (n*n - n) / 2
end

def pairings
@pairings ||= compute_pairings
end

private

def more_tired(played, pair)
appearances = played.flatten
pair.sort_by {|comp| appearances.select { |e| e == comp }.length}.last
end

def compute_pairings
pairings = []
picks = competitors.dup
while pairings.length < full_size
trial_pair = picks[0..1].sort
if pairings.include?(trial_pair)
more_tired = more_tired(pairings, trial_pair)
picks.delete(more_tired)
picks << more_tired
else
pairings << trial_pair
picks << picks.shift
picks << picks.shift
end
end
pairings
end
end
puts "For n = 4"
RoundRobinPairsGenerator.new(4).pairings.each { |p| p p }
puts
puts "For n = 10"
RoundRobinPairsGenerator.new(10).pairings.each { |p| p p }

produces:
For n = 4
[1, 2]
[3, 4]
[1, 3]
[2, 4]
[1, 4]
[2, 3]

For n = 10
[1, 2]
[3, 4]
[5, 6]
[7, 8]
[9, 10]
[1, 3]
[4, 5]
[6, 7]
[8, 9]
[2, 10]
[1, 4]
[5, 7]
[8, 10]
[2, 3]
[1, 6]
[5, 9]
[2, 8]
[3, 6]
[7, 9]
[4, 10]
[1, 5]
[2, 7]
[3, 5]
[4, 8]
[6, 9]
[1, 10]
[3, 9]
[2, 4]
[5, 10]
[6, 8]
[1, 9]
[4, 7]
[2, 5]
[3, 8]
[7, 10]
[4, 6]
[2, 9]
[1, 8]
[6, 10]
[3, 7]
[1, 7]
[3, 10]
[2, 6]
[5, 8]
[4, 9]

--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denh...

Milo Thurston

10/16/2007 6:51:00 PM

Rick Denatale wrote:
> def compute_pairings
> pairings = []
> picks = competitors.dup
> while pairings.length < full_size
> trial_pair = picks[0..1].sort
> if pairings.include?(trial_pair)
> more_tired = more_tired(pairings, trial_pair)
> picks.delete(more_tired)
> picks << more_tired
> else
> pairings << trial_pair
> picks << picks.shift
> picks << picks.shift
> end
> end
> pairings
> end
> end

That is very interesting - I would never have thought of it.
Many thanks!

--
Posted via http://www.ruby-....

Yossef Mendelssohn

10/16/2007 8:50:00 PM

On Oct 16, 1:22 pm, "Rick DeNatale" <rick.denat...@gmail.com> wrote:
> On 10/16/07, Milo Thurston <knir...@gmail.com> wrote:
>
>
>
> > Sport fencing competitions are organised in pools, where every fencer
> > fences every other and the total score is totted up at the end. Sheets
> > like this are used to keep track of which bouts have been played and
> > what the score is:
> >http://www.soton.ac.uk/~fencing/file...
> > These sheets show an order of bouts for between 4-7 fencers, a typical
> > number in a pool. An impending competition* got me wondering how one
> > might use Ruby to generate those lists of bouts. A simple list of what
> > bouts need to be fought is easy, and I wrote a simple script that
> > produces an array of the following values for any number of contestants
> > (in this case 4):
>
> > 1 - 2
> > 1 - 3
> > 1 - 4
> > 2 - 3
> > 2 - 4
> > 3 - 4
>
> > The difficult bit is that fencers need to be given a rest between bouts
> > if possible, so this order won't do. Simply randomising this array may
> > still mean someone having to do more than one fight in a row. Not having
> > a mathematical background I can't think of a suitable method to approach
> > this, and if anyone could suggest some hints I'd be interested to know.
>
> How about:
>
> class RoundRobinPairsGenerator
>
> attr_reader :competitors, :full_size
>
> def initialize(n)
> @competitors = (1..n).to_a
> @full_size = (n*n - n) / 2
> end
>
> def pairings
> @pairings ||= compute_pairings
> end
>
> private
>
> def more_tired(played, pair)
> appearances = played.flatten
> pair.sort_by {|comp| appearances.select { |e| e == comp }.length}.last
> end
>
> def compute_pairings
> pairings = []
> picks = competitors.dup
> while pairings.length < full_size
> trial_pair = picks[0..1].sort
> if pairings.include?(trial_pair)
> more_tired = more_tired(pairings, trial_pair)
> picks.delete(more_tired)
> picks << more_tired
> else
> pairings << trial_pair
> picks << picks.shift
> picks << picks.shift
> end
> end
> pairings
> end
> end
> puts "For n = 4"
> RoundRobinPairsGenerator.new(4).pairings.each { |p| p p }
> puts
> puts "For n = 10"
> RoundRobinPairsGenerator.new(10).pairings.each { |p| p p }
>
> produces:
> For n = 4
> [1, 2]
> [3, 4]
> [1, 3]
> [2, 4]
> [1, 4]
> [2, 3]
>
> For n = 10
> [1, 2]
> [3, 4]
> [5, 6]
> [7, 8]
> [9, 10]
> [1, 3]
> [4, 5]
> [6, 7]
> [8, 9]
> [2, 10]
> [1, 4]
> [5, 7]
> [8, 10]
> [2, 3]
> [1, 6]
> [5, 9]
> [2, 8]
> [3, 6]
> [7, 9]
> [4, 10]
> [1, 5]
> [2, 7]
> [3, 5]
> [4, 8]
> [6, 9]
> [1, 10]
> [3, 9]
> [2, 4]
> [5, 10]
> [6, 8]
> [1, 9]
> [4, 7]
> [2, 5]
> [3, 8]
> [7, 10]
> [4, 6]
> [2, 9]
> [1, 8]
> [6, 10]
> [3, 7]
> [1, 7]
> [3, 10]
> [2, 6]
> [5, 8]
> [4, 9]
>
> --
> Rick DeNatale
>
> My blog on Rubyhttp://talklikeaduck.denh...

Nice.

Just in case you (or anyone else) was interested, I quickly threw
together something that would create the simple pairings (1.upto(x) { |
i| (x+1).upto(x) { |j| ... } }) and then attempt to re-order it
afterwards. I didn't have high hopes for it, and it didn't seem to
work for any number (well, any number > 2).

I haven't bothered to work out a mathematical proof or anything, but I
believe it's impossible to generate the pairings that way and then re-
order them. It really should be done this way, taking the rest period
into account when creating the pairings.

--
-yossef

comp.lang.ruby

Ruby for arranging fencing competitions

Milo Thurston

Jesús Gabriel y Galán

Milo Thurston

Rick DeNatale

Milo Thurston

Yossef Mendelssohn

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