JavaScript的数组旋转（） [英] JavaScript Array rotate()

问题描述

我想知道什么是旋转的JavaScript 阵列的最有效方法。

I was wondering what was the most efficient way to rotate a JavaScript array.

我想出了这个解决方案，其中正 N 旋转阵列的权利，以及负 N 向左（ -length＆LT; N＆LT;长度）

I came up with this solution, where a positive n rotates the array to the right, and a negative n to the left (-length < n < length) :

Array.prototype.rotate = function( n ) {
  this.unshift( this.splice( n, this.length ) )
}

然后可以这样使用：

Which can then be used this way:

var months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
months.rotate( new Date().getMonth() )

以上我原来的版本有一个缺陷，如克里斯托夫贝娄的评论中指出，正确的版本是（额外的回报允许链接）：

My original version above has a flaw, as pointed out by Christoph in the comments bellow, a correct version is (the additional return allows chaining):

Array.prototype.rotate = function( n ) {
  this.unshift.apply( this, this.splice( n, this.length ) )
  return this;
}

有没有更紧凑和/或更快的解决方案，可能是一个JavaScript框架的背景下？ （无建议版本的吼叫或者是更紧凑或更快）。

Is there a more compact and/or faster solution, possibly in the context of a JavaScript framework? (none of the proposed versions bellow is either more compact or faster)

有一个数组旋转内置的JavaScript框架在那里？ （仍然没有任何人回答）

Is there any JavaScript framework out there with an array rotate built-in? (Still not answered by anyone)

推荐答案

类型安全，通用版本，变异的数组：

Type-safe, generic version which mutates the array:

Array.prototype.rotate = (function() {
    // save references to array functions to make lookup faster
    var push = Array.prototype.push,
        splice = Array.prototype.splice;

    return function(count) {
        var len = this.length >>> 0, // convert to uint
            count = count >> 0; // convert to int

        // convert count to value in range [0, len)
        count = ((count % len) + len) % len;

        // use splice.call() instead of this.splice() to make function generic
        push.apply(this, splice.call(this, 0, count));
        return this;
    };
})();

在的意见，让募集拼接（）的问题是，code不支持超载推（）和。我不认为这是非常有用的（见注释），但一个快速解决方案（一个黑客颇有几分，虽然）将取代行

In the comments, Jean raised the issue that the code doesn't support overloading of push() and splice(). I don't think this is really useful (see comments), but a quick solution (somewhat of a hack, though) would be to replace the line

push.apply(this, splice.call(this, 0, count));

这一个：

(this.push || push).apply(this, (this.splice || splice).call(this, 0, count));

---

使用的unshift（）而不是推（）是接近两倍的速度在Opera 10，而差异在FF可以忽略不计;在code：

---

Using unshift() instead of push() is nearly twice as fast in Opera 10, whereas the differences in FF were negligible; the code:

Array.prototype.rotate = (function() {
    var unshift = Array.prototype.unshift,
        splice = Array.prototype.splice;

    return function(count) {
        var len = this.length >>> 0,
            count = count >> 0;

        unshift.apply(this, splice.call(this, count % len, len));
        return this;
    };
})();

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