The idea is simple, I have like 2000 rows of data about the matches between teams. I want to order the teams by strength strange comparing to each other based on results of the matches they had in the past.
Lets say here is the matches that already happened:
1 vs 2 => 2 Won
2 vs 1 => 2 Won
3 vs 1 => 1 Won
4 vs 3 => 3 Won
5 vs 3 => 5 Won
1 vs 5 => 5 Won
Now based on this information I want to order the teams. Any idea or known algorithm for this? The result should be something like:
1st: Team 2
2nd: Team 5
3rd: Team 1
4th: Team 3
5th: Team 4
ofc the data here is very limited and simple.
Data:
Data contains all the games in last year from all the leagues. Two team may have no game, or one or more game with each other. There is also a possibility for cycles. Like A vs B => B, B vs C => C and C vs A => A as these are real world data. What I want is a way to sort the data and guess their strength related to each other (Not to the games. Like adding or removing score based on their win) and what is important for me is the end result. So if this mean removing some matches from the equation to calculate the result better, I am ok with it.
Accuracy Note:
Based on the information, there is no indication if team 2 is better than team 5 or vice versa. So it would be great if we can find a way to calculate a number as the weight of position or something like that.
This answers assume there is a proper order (and no "cycles") in the winners pairs.
Seems to me like you are looking for a topological sort in a DAG. This can be solved in linear time.
The vertices are the teams, and the edges are the relations of who won for each pair.
Regarding the accuracy: that could be a bit complicated, but one (partial) approach to handle it could be:
During the topological sort, when you have k choices at some point, chose one at random, and give all possibilities probability 1/k.
The probability issue is just a raw tryout, you will need to tweak it better to get exactly what you wanted to handle all cases properly.
You should have a dictionary/lookup for team->points. Whenever a team wins add a point. If it loses subtract one point.
After you did this for all games (two operations per game) you may sort this lookup with "points" as the sort key.
If two teams have the same number of points you may indicate this like (same rank as ...)
There is no such thing as "accuracy". A team is better as another or has the same rank.
If the game produces more detailed results like "number of goals goals" you may create a second ranking based on "goal difference" using a very similar approach.
Related
I'm organizing a game tournament in a week. I began thinking about the best way to mathematically arrange the teams (so that they are really even, thus more competitive). So here's the data:
20 players in the event
Each player is assigned a skill level (high number = skilled)
4 teams of 5 players each (although I'd prefer to build a algorithm that takes these as
variables)
I'm using a computer to solve the problem
So, I have 20 players. I'd like to generate 4 teams with 5 players each. To do this, I'd like to generate a list of all possible team combinations. To evaluate a team combination, I:
Generate a combination of teams (a match)
Sum the total skill for each team based off the players in that team
Compare each team to each other, the highest difference between any two teams in the match is the "tolerance" level for that match. If the tolerance level is higher than a certain cap, the match is discarded
My current approach is to generate a base X number that is N digits long, where X is the number of teams I want, and N is the number of players. Then increment the base X number by 1, I'll get every possible team combination, and I can generate a list of matches that have low tolerance values.
The problem with this, as you probably know, is for 4 teams with 20 players, that's (4-1)^20 in base 3, which is 1E12 matches to check through. (This takes a long time on my computer). Is there a mathematical way to simplify this calculation to be doable in a short period of time?
By current method also allows for the possibility of uneven players spread across the number of teams, which is preferable. If this can't be present with a highly performant algorithm, then it's okay not to use it.
Try following approach:
For teams 1 to 4: Take the strongest player from the remaining
The the same in another direction: from 4 to 1
Again 1 to 4
Again 4 to 1
In the last round use random
This works well when player skills are distributed more or less evenly. If not, then the probability of bigger differences between teams is higher.
I have a specific number of teams. I want every team to play exactly 4 matches with 4 different opponents at 4 specified times.
The complication arises from that no team can play 2 different matches at the same time.
For example if team 1 is playing like this
team1 vs team2, team1 vs team3, team1 vs team4, team1 vs team5
then team2 already has the first time slot occupied so team2 can play like this
(team2 vs team1), team2 vs team3, team2 vs team4, team2 vs team5
But here the problem arises, team3 will play in the second time slot with team1 and team2 and this can not be done.
I do not know what this algorithm can be called, but I am searching for algorithm to implement this.
I made a search to find round-robin and other tournament like matching algorithm and also the marriage problem, but I think my problem is different. Please correct me if I am wrong.
Any help is greatly appreciated.
I have concluded there is no solution if the number of teams is odd. Let N be the number of teams. We need a total of N*4/2 matches, four matches per team but each match counts for two teams. To do N*2 matches in four time slots we must average N/2 matches per slot. We can do at most floor(N/2) matches at a time. If N is odd, floor(N/2) < N/2.
Would a solution that only works for even N, if it exists, be useful?
A simple algorithm:
Round 1
1 2 3 4
8 7 6 5
Then rotate places 2-8...
Round 2
1 8 2 3
7 6 5 4
Round 3
1 7 8 2
6 5 4 3
http://en.wikipedia.org/wiki/Round-robin_tournament#Scheduling_algorithm
(If there is an odd number, one can extend the this by adding a dummy pairing to indicate a bye, but then as Patricia Shanahan notes, not every team would play every round. So an even number of teams and at least six teams are needed to fit the requirements.)
This algorithm will work for any number of teams.
Suppose there are 6 teams in a tournament.
This solution basically tells you how to fill the 6x6 matrix, and each entry in the matrix is the match between the teams in the row vs column.
Consider few rules in the algorithm
1. Increment value in the matrix from left to right and top to bottom. mat[0][0] = 1
2. Whenever i == j, then fill the matrix at [n-1][j] instead at [i][j]. Basically, no entry will be there at i==j
3. And whenever entry in the matrix reaches to 6, make it 1
We will follow this rule and start filling the matrix from [0][0] column-wise.
Means first we will fill every row of 0th column then move to 1st column and so.
- At [0][0], apply rule 2. So fill mat[n-1][0] = 0
- At mat[1][0], fill next number ie 2 and similarly for [2][0], [3][0], [4][0]
- And now column 1, starts with value 2
- mat[1][0] = 2;
- At mat[1][1] apply rule 2, fill last row of current column ie mat[n-1][1] = 3
If you want that every team should play only one game with other team, use lower triangle.
And if you want that every team should play 2 games with other teams, one home and away use both lower and upper triangle.
Hope you guys understand my solution.
Cheers
I'm working in Ruby, but I think this question is best asked agnostic of language. It may be assumed that we have access to basic list/array functions, as well as a "random" number generator. Here's what I'd like to be able to do:
Given a collection of n teams, with n even,
Randomly pair each team with an opponent, such that every team is part of exactly one pair. Call this ROUND 1.
Randomly generate n-2 subsequent rounds (ROUND 2 through ROUND n-1) such that:
Each round has the same property as the first (every team is a
member of one pair), and
After all the rounds, every team has faced every other team exactly once.
I imagine that algorithms for doing exactly this must be well known, but as a self-taught coder I'm having trouble figuring out how to find them.
I belive You are describing a round robin tournament. The wikipedia page gives an algorithm.
If You need a way to randomize the schedule, randomize team order, round order, etc.
Well not sure if this is the most efficient algorithm but:
Randomly assign N teams into two lists of same length n/2 (List1, List2)
Starting with i = 0:
Create pairs: List1[i],List2[i] = a team pair
Repeat for i = 1-> (n/2-1)
For rounds 2-> n/2-1:
Rotate List2, so that the first team in List2 is now at the end.
Repeat steps 2 through 5, until List2 has been cycled once.
This link was very helpful to me the last time I wrote a round robin scheduling algorithm. It includes a C implementation of a first fit algorithm for round robin pairings.
http://www.devenezia.com/downloads/round-robin/
In addition to the algorithm, he has some helpful links to other aspects of tournament scheduling (balancing home and away games, as well as rotating teams across fields/courts).
Note that you don't necessarily want a "random" order to the pairings in all cases. If, for example, you were scheduling a round robin soccer league for 8 games that only had 6 teams, then each team is going to have to play two other teams twice. If you want to make a more enjoyable season for everyone, you have to start worrying about seeding so that you don't have your top 2 teams clobbering the two weakest teams in their last two games. You'd be better off arranging for the extra games to be paired against teams of similar strength/seeding.
Based on info I found through Maniek's link, I went with the following:
A simple round robin algorithm that
a. Starts with pairings achieved by zipping [0,...,(n-1)/2] and [(n-1)/2 + 1,..., n-1]. (So, if n==10, we have 0 paired with 5, 1 with 6, etc.)
b. Rotates all but one team n-2 times clockwise until all teams have played each other. (So in round 2 we pair 1 with 6, 5 with 7, etc.)
Randomly assigns one of [0,..., n-1] to each of the teams.
I have a data set of players' skill ranking, age and sex and would like to create evenly matched teams.
Teams will have the same number of players (currently 8 teams of 12 players).
Teams should have the same or similar male to female ratio.
Teams should have similar age curve/distribution.
I would like to try this in Haskell but the choice of coding language is the least important aspect of this problem.
This is a bin packing problem, or a multi-dimensional knapsack problem. Björn B. Brandenburg has made a bin packing heuristics library in Haskell that you may find useful.
You need something like...
data Player = P { skill :: Int, gender :: Bool, age :: Int }
Decide on a number of teams n (I'm guessing this is a function of the total number of players).
Find the desired total skill per team:
teamSkill n ps = sum (map skill ps) / n
Find the ideal gender ratio:
genderRatio ps = sum (map (\x -> if gender x then 1 else 0)) / length ps
Find the ideal age variance (you'll want the Math.Statistics package):
ageDist ps = pvar (map age ps)
And you must assign the three constraints some weights to come up with a scoring for a given team:
score skillW genderW ageW team = skillW * sk + genderW * g + ageW * a
where (sk, (g, a)) = (teamSkill 1 &&& genderRatio &&& ageDist) team
The problem reduces to the minimization of the difference in scores between teams. A brute force approach will take time proportional to Θ(nk−1). Given the size of your problem (8 teams of 12 players each), this translates to about 6 to 24 hours on a typical modern PC.
EDIT
An approach that may work well for you (since you don't need an exact solution in practise) is simulated annealing, or continual improvement by random permutation:
Pick teams at random.
Get a score for this configuration (see above).
Randomly swap players between two or more teams.
Get a score for the new configuration. If it's better than the previous one, keep it and recurse to step 3. Otherwise discard the new configuration and try step 3 again.
When the score has not improved for some fixed number of iterations (experiment to find the knee of this curve), stop. It's likely that the configuration you have at this point will be close enough to the ideal. Run this algorithm a few times to gain confidence that you have not hit on some local optimum that is considerably worse than ideal.
Given the number of players per team and the gender ration (which you can easily compute). The remaining problem is called n-partition problem, which is unfortunately NP-complete and thus very hard to solve exactly. You will have to use approximative or heuristic allgorithms (evolutionary algorithms), if your problem size is too big for a brute force solution. A very simple approximation would be sorting by age and assign in an alternating way.
Assign point values to the skill levels, gender, and age
Assign the sum of the points for each criteria to each player
Sort players by their calculated point value
Assign the next player to the first team
Assign players to the second team until it has >= total points than the first team or the team reaches the maximum players.
Perform 5 for each team, looping back to the first team, until all players are assigned
You can tweak the skill level, gender, and age point values to change the distribution of each.
Lets say you have six players (for a simple example). We can use the same algorithm which pairs opponents in single-elimination tournaments and adapt that to generate "even" teams based on any criteria you choose.
First rank your players best-to-worst. Don't take this too literally. You want a list of players sorted by the criteria you wish to separate them.
Why?
Let's look at single elimination tournaments for a second. The idea of using an algorithm to generate optimal single-elimination matches is to avoid the problem of the "top players" meeting too soon in the tournament. If top players meet too soon, one of the top players will be eliminated early on, making the tournament less interesting. We can use this "optimal" pairing to generate teams in which the "top" players are spread out evenly across the teams. Then spread out the the second top players, etc, etc.
So list you players by the criteria you want them separated: men first, then women... sorted by age second. We get (for example):
Player 1: Male - 18
Player 2: Male - 26
Player 3: Male - 45
Player 4: Female - 18
Player 5: Female - 26
Player 6: Female - 45
Then we'll apply the single-elimination algorithm which uses their "rank" (which is just their player number) to create "good match ups".
The single-elimination tournament generator basically works like this: take their rank (player number) and reverse the bits (binary). This new number you come up with become their "slot" in the tournament.
Player 1 in binary (001), reversed becomes 100 (4 decimal) = slot 4
Player 2 in binary (010), reversed becomes 010 (2 decimal) = slot 2
Player 3 in binary (011), reversed becomes 110 (6 decimal) = slot 6
Player 4 in binary (100), reversed becomes 001 (1 decimal) = slot 1
Player 5 in binary (101), reversed becomes 101 (5 decimal) = slot 5
Player 6 in binary (110), reversed becomes 011 (3 decimal) = slot 3
In a single-elimination tournament, slot 1 plays slot 2, 3-vs-4, 5-vs-6. We're going to uses these "pair ups" to generate optimal teams.
Looking at the player number above, ordered by their "slot number", here is the list we came up with:
Slot 1: Female - 18
Slot 2: Male - 26
Slot 3: Female - 45
Slot 4: Male - 18
Slot 5: Female - 26
Slot 6: Male - 45
When you split the slots up into teams (two or more) you get the players in slot 1-3 vs players in slot 4-6. That is the best/optimal grouping you can get.
This technique scales very well with many more players, multiple criteria (just group them together correctly), and multiple teams.
Idea:
Sort players by skill
Assign best players in order (i.e.: team A: 1st player, team B: 2nd player, ...)
Assign worst players in order
Loop on 2
Evaluate possible corrections and perform them (i.e.: if team A has a total skill of 19 with a player with skill 5 and team B has a total skill of 21 with a player with skill 4, interchange them)
Evaluate possible corrections on gender distribution and perform them
Evaluate possible corrections on age distribution and perform them
Almost trivial approach for two teams:
Sort all player by your skill/rank assessment.
Assign team A the best player.
Assign team B the next two best players
Assign team A the next two best players
goto 3
End when you're out of players.
Not very flexible, and only works on one column ranking, so it won't try to get similar gender or age profiles. But it does make fair well matched teams if the input distribution is reasonably smooth. Plus it doesn't always end with team A have the spare player when there are an odd number.
Well,
My answer is not about scoring strategies of teams/players because all the posted are good, but I would try a brute force or a random search approach.
I don't think it's worth create a genetic algorithm.
Regards.
I have a project for school where I have to come up with an algorithm for scheduling 4 teams to play volleyball on one court, such that each team gets as close to the same amount of time as possible to play.
If you always have the winners stay in and rotate out the loser, then the 4th ranked team will never play and the #1 team always will.
The goal is to have everybody play the same amount of time.
The simplest answer is team 1 play team 2, then team 3 play team 4 and keep switching, but then team 1 never gets to play team 3 or 4 and so on.
So I'm trying to figure out an algorithm that will allow everybody to play everybody else at some point without having one team sit out a lot more than any other team.
Suggestions?
How about this: Make a hashtable H of size NC2, in this case, 6. It looks like:
H[12] = 0
H[13] = 0
H[14] = 0
H[23] = 0
H[24] = 0
H[34] = 0
I am assuming it would be trivial to generate the keys.
Now to schedule a game, scan through the hash and pick the key with the lowest value (one pass). The teams denoted by the key play the game and you increment the value by one.
EDIT:
To add another constraint that no team should wait too long, make another hash W:
W[1] = 0
W[2] = 0
W[3] = 0
W[4] = 0
After every game increment the W value for the team that did not play, by one.
Now when picking up the least played team if there are more than one team combo with low play score, take help from this hash to determine which team must play next.
well you should play 1-2 3-4, 1-3 2-4, 1-4 2-3 and then start all over again.
If there are N teams and you want all pairs of them to play once, then there are "N choose 2" = N*(N-1)/2 games you need to run.
To enumerate them, just put the teams in an ordered list and have the first team play every other team, then have the second team play all the teams below it in the list, and so on. If you want to spread the games out so teams have similar rest intervals between games, then see Knuth.
Check out the wikipedia entry on round robin scheduling.
pretend it's a small sports league, and repeat the "seasons"...
(in most sports leagues in Europe, all teams play against all other teams a couple of times during a season)
The REQUIREMENTS for the BALANCED ROUND ROBIN algorithm, for the Team championship scheduling may be found here:
Constellation Algorithm - Balanced Round Robin
The requirements of the algorithm can be defined by these four constraints:
1) All versus all
Each team must meet exactly once, and once only, the other teams in the division/ league.
If the division is composed of n teams, the championship takes place in the n-1 rounds.
2) Alternations HOME / AWAY rule
The sequence of alternations HOME / AWAY matches for every teams in the division league, should be retained if possible. For any team in the division league at most once in the sequence of consecutive matches HAHA, occurs the BREAK of the rhythm, i.e. HH or AA match in the two consecutive rounds.
3) The rule of the last slot number
The team with the highest slot number must always be positioned in the last row of the grid. For each subsequent iteration the highest slot number of grid alternates left and right position; left column (home) and right (away).
The system used to compose the league schedule is "counter-clockwise circuit." In the construction of matches in one round of the championship, a division with an even number of teams. If in a division is present odd number of teams, it will be inserted a BYE/Dummy team in the highest slot number of grid/ring.
4) HH and AA non-terminal and not initial
Cadence HH or AA must never happen at the beginning or at the end of the of matches for any team in the division.