Pairing array elements in ruby

Let's say i have an array called teams.

I want to plan matches for every team with every other team.

This is almost what i want except that same matches are added twice:

teams.each do |red_team|
  teams.each do |blue_team|
    if red_开发者_如何学Cteam != blue_team
      @planned_matches << Match.new(red_team, blue_team)
    end
  end
end

How to do that?

In Ruby 1.8.7+ you can use Array#combination:

teams = %w(A B C D)
matches = teams.combination(2).to_a

In 1.8.6, you can use Facets to do the same:

require 'facets/array/combination'
# Same code as above.

check if it works

for i in 0..teams.length-1
  if i != teams.last
    for j in (i+1)..teams.length-1
      @planned_matches << Match.new(teams[i], teams[j])
    end
  end
end

EXAMPLE

teams = ['GERMANY', 'NETHERLAND', 'PARAGUAY', 'ARGENTINA']
for i in 0..teams.length-1
  if i != teams.last
    for j in (i+1)..teams.length-1
      puts " #{teams[i]}  Vs  #{teams[j]}"
    end
  end
end

O/P

 GERMANY  Vs  NETHERLAND
 GERMANY  Vs  PARAGUAY
 GERMANY  Vs  ARGENTINA
 NETHERLAND  Vs  PARAGUAY
 NETHERLAND  Vs  ARGENTINA
 PARAGUAY  Vs  ARGENTINA

In your class Match, assuming internal attributes are red and blue

class Match
#...
  def ==(anOther)
    red == anOther.blue and anOther.red == blue
  end
#...
end

and the loop :

teams.each do |red_team|
  teams.each do |blue_team|
    if red_team != blue_team
      new_match = Match.new(red_team, blue_team)
      planned_matches << new_match if !planned_matches.include?(new_match)
    end
  end
end

Explanation :

The include? function of Array uses the == methods, so you just have to override it and giving it the behaviour you want for your Matches.