旋转JavaScript中数组中的元素 [英] Rotate the elements in an array in JavaScript
问题描述
我想知道旋转JavaScript数组的最有效方法是什么.
I was wondering what was the most efficient way to rotate a JavaScript array.
我想出了这个解决方案,其中正数n
将数组向右旋转,而负数n
向左旋转(-length < n < length
):
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.rotateRight = function( n ) {
this.unshift( this.splice( n, this.length ) );
}
然后可以通过以下方式使用:
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() );
我上面的原始版本有一个缺陷,正如下面的注释中 Christoph 所指出的那样,正确的版本是(额外的收益允许链接):
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.rotateRight = function( n ) {
this.unshift.apply( this, this.splice( n, this.length ) );
return this;
}
是否可能在JavaScript框架的上下文中提供更紧凑和/或更快速的解决方案? (以下任何一种建议的版本都不会更紧凑或更快速)
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)
是否存在带有内置数组旋转功能的JavaScript框架? (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
更改数组的类型安全的通用版本:
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;
};
})();
在评论中,Jean提出了一个问题,该代码不支持push()
和splice()
的重载.我不认为这真的有用(请参阅评论),但是一种快速的解决方案(虽然有点hack)将替换该行
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));
与此:
(this.push || push).apply(this, (this.splice || splice).call(this, 0, count));
在Opera 10中,使用unshift()
代替push()
的速度几乎快一倍,而FF的差异可以忽略不计.代码:
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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