sharing/swapping items between lists

Aaron Brady castironpi at
Tue Apr 14 06:52:37 CEST 2009

On Apr 13, 10:04 am, Ross <ross.j... at> wrote:
> On Apr 11, 1:10 pm, a... at (Aahz) wrote:
> > In article <4fd78ac3-ba83-456b-b768-3a0043548... at>,
> > Ross  <ross.j... at> wrote:
> > >I'm trying to design an iterator that produces two lists. The first
> > >list will be a list of unique pairings and the second will be a list
> > >of items that weren't used in the first list. After each round, the
> > >items that weren't used in the round before will get put back in and
> > >the second list will be populated with unique items.
> > How do you specify what goes into the first list?  Based on your
> > description, I would have expected that the output from the first
> > iteration would be
> > ( [(1,2),(3,4),(5,6)], [7,8] )
> > Regardless of the actual algorithm, if you are returning items one at a
> > time and maintaining state in a computation, you probably want to use a
> > generator.
> > --
> > Aahz (a... at           <*>
> > Why is this newsgroup different from all other newsgroups?
> I'm example was probably a bad one. A better example of
> output I would like would be something like [[1,2],[3,4],[5,6]] and
> then for the leftovers list [7,8,9,10 etc]. What I'm trying to do is
> produce some sort of round robin algorithm for tennis that is
> constrained by the number of courts available each week. So if there
> are only 3 courts available for a singles league and 10 people have
> signed up, 4 players will have a bye each week. I want my algorithm to
> produce unique matchups each week and also give each player the same
> angle?

Take 3 people, 1 court.

a, b -- c
a, c -- b
b, c -- a

Take 4 people, 1 court.

a, b -- c, d
c, d -- a, b
a, c -- b, d
b, d -- a, c

Take 4 people, 2 courts.

ab, cd
ac, bd
ad, bc

Take 5 people, 1 court.

ab - cde
cd - abe
ae - bcd
bc - ade
de - abc

ac - bde
bd - ace
ce - abd
ad - bce
be - acd

You can work more by hand and post them if you want.  There are known
ways to produce the list on the left out of order.  It might take
multiple steps, that is, choose 2 then 2 more, instead of just choose
4.  Then, you need to arrange it so the player with most court time
has at most one more match than the player with the least court time,
after each week.  We could help with that too.  Something tells me
there's a regular expression for it.

Do you need to account for newcomers after the rotation has started,
departers, favorites, skill, etc.?

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