0425ebefe7
Cleaned up the current snippets for consistency and minor problems, added multiple tags to most of them, archived a few.
45 lines
1.7 KiB
Markdown
45 lines
1.7 KiB
Markdown
### elo
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Computes the new ratings between two or more opponents using the [Elo rating system](https://en.wikipedia.org/wiki/Elo_rating_system). It takes an array
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of pre-ratings and returns an array containing post-ratings.
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The array should be ordered from best performer to worst performer (winner -> loser).
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Use the exponent `**` operator and math operators to compute the expected score (chance of winning).
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of each opponent and compute the new rating for each.
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Loop through the ratings, using each permutation to compute the post-Elo rating for each player in a pairwise fashion.
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Omit the second argument to use the default `kFactor` of 32.
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```js
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const elo = ([...ratings], kFactor = 32, selfRating) => {
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const [a, b] = ratings;
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const expectedScore = (self, opponent) => 1 / (1 + 10 ** ((opponent - self) / 400));
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const newRating = (rating, i) =>
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(selfRating || rating) + kFactor * (i - expectedScore(i ? a : b, i ? b : a));
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if (ratings.length === 2) {
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return [newRating(a, 1), newRating(b, 0)];
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} else {
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for (let i = 0; i < ratings.length; i++) {
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let j = i;
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while (j < ratings.length - 1) {
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[ratings[i], ratings[j + 1]] = elo([ratings[i], ratings[j + 1]], kFactor);
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j++;
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}
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}
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}
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return ratings;
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};
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```
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```js
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// Standard 1v1s
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elo([1200, 1200]); // [1216, 1184]
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elo([1200, 1200], 64); // [1232, 1168]
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// 4 player FFA, all same rank
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elo([1200, 1200, 1200, 1200]).map(Math.round); // [1246, 1215, 1185, 1154]
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/*
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For teams, each rating can adjusted based on own team's average rating vs.
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average rating of opposing team, with the score being added to their
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own individual rating by supplying it as the third argument.
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*/
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```
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