From d9fe4b84cc22da26b03815732773e4c7a7e17b2d Mon Sep 17 00:00:00 2001 From: Bill Mei Date: Mon, 25 Dec 2017 18:43:55 -0800 Subject: [PATCH 1/3] User Fisher-Yates shuffle implementation --- snippets/shuffle.md | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/snippets/shuffle.md b/snippets/shuffle.md index 27d7fd783..c23d5296a 100644 --- a/snippets/shuffle.md +++ b/snippets/shuffle.md @@ -1,10 +1,20 @@ ### shuffle -Randomizes the order of the values of an array. +Randomizes the order of the values of an array, in place. -Use `Array.sort()` to reorder elements, using `Math.random()` in the comparator. +Users the Fisher-Yates reorder the elements, based on the [Lodash implementation](https://github.com/lodash/lodash/blob/b2ea6b1cd251796dcb5f9700c4911a7b6223920b/shuffle.js). ```js -const shuffle = arr => arr.sort(() => Math.random() - 0.5); +const shuffle = (arr = []) => { + let i = -1; + const lastIndex = arr.length - 1; + while (++i < arr.length) { + const rand = i + Math.floor(Math.random() * (lastIndex - i + 1)); + const value = arr[rand]; + arr[rand] = arr[i]; + arr[i] = value; + } + return arr +}; // shuffle([1,2,3]) -> [2,3,1] ``` From bb8e1a28c09558cb1458372a60cfae30767a0511 Mon Sep 17 00:00:00 2001 From: David Wu Date: Tue, 26 Dec 2017 14:23:44 +0100 Subject: [PATCH 2/3] fix typo --- snippets/shuffle.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/snippets/shuffle.md b/snippets/shuffle.md index c23d5296a..99a0e25d6 100644 --- a/snippets/shuffle.md +++ b/snippets/shuffle.md @@ -2,7 +2,7 @@ Randomizes the order of the values of an array, in place. -Users the Fisher-Yates reorder the elements, based on the [Lodash implementation](https://github.com/lodash/lodash/blob/b2ea6b1cd251796dcb5f9700c4911a7b6223920b/shuffle.js). +Uses the Fisher-Yates algoritm to reorder the elements of the array, based on the [Lodash implimentation](https://github.com/lodash/lodash/blob/b2ea6b1cd251796dcb5f9700c4911a7b6223920b/shuffle.js) ```js const shuffle = (arr = []) => { From f1bab2570c44ba346dee69ffe9f26ede7ba26775 Mon Sep 17 00:00:00 2001 From: David Wu Date: Tue, 26 Dec 2017 14:24:04 +0100 Subject: [PATCH 3/3] Shorten algorithm --- snippets/shuffle.md | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-) diff --git a/snippets/shuffle.md b/snippets/shuffle.md index 99a0e25d6..54687f67f 100644 --- a/snippets/shuffle.md +++ b/snippets/shuffle.md @@ -5,16 +5,13 @@ Randomizes the order of the values of an array, in place. Uses the Fisher-Yates algoritm to reorder the elements of the array, based on the [Lodash implimentation](https://github.com/lodash/lodash/blob/b2ea6b1cd251796dcb5f9700c4911a7b6223920b/shuffle.js) ```js -const shuffle = (arr = []) => { - let i = -1; - const lastIndex = arr.length - 1; - while (++i < arr.length) { - const rand = i + Math.floor(Math.random() * (lastIndex - i + 1)); - const value = arr[rand]; - arr[rand] = arr[i]; - arr[i] = value; +const shuffle = ([...arr]) => { + let m = arr.length; + while (m) { + const i = Math.floor(Math.random() * m--); + [arr[m], arr[i]] = [arr[i], arr[m]]; } - return arr + return arr; }; // shuffle([1,2,3]) -> [2,3,1] ```