Delete elo

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snippets/elo.md

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----
-title: elo
-tags: math,array,advanced
----
-
-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
-of pre-ratings and returns an array containing post-ratings.
-The array should be ordered from best performer to worst performer (winner -> loser).
-
-- Use the exponent `**` operator and math operators to compute the expected score (chance of winning) of each opponent and compute the new rating for each.
-- Loop through the ratings, using each permutation to compute the post-Elo rating for each player in a pairwise fashion.
-- Omit the second argument to use the default `kFactor` of 32.
-
-```js
-const elo = ([...ratings], kFactor = 32, selfRating) => {
-  const [a, b] = ratings;
-  const expectedScore = (self, opponent) => 1 / (1 + 10 ** ((opponent - self) / 400));
-  const newRating = (rating, i) =>
-    (selfRating || rating) + kFactor * (i - expectedScore(i ? a : b, i ? b : a));
-  if (ratings.length === 2) return [newRating(a, 1), newRating(b, 0)];
-
-  for (let i = 0, len = ratings.length; i < len; i++) {
-    let j = i;
-    while (j < len - 1) {
-      j++;
-      [ratings[i], ratings[j]] = elo([ratings[i], ratings[j]], kFactor);
-    }
-  }
-  return ratings;
-};
-```
-
-```js
-// Standard 1v1s
-elo([1200, 1200]); // [1216, 1184]
-elo([1200, 1200], 64); // [1232, 1168]
-// 4 player FFA, all same rank
-elo([1200, 1200, 1200, 1200]).map(Math.round); // [1246, 1215, 1185, 1154]
-/*
-For teams, each rating can adjusted based on own team's average rating vs.
-average rating of opposing team, with the score being added to their
-own individual rating by supplying it as the third argument.
-*/
-```