JavaScript中的循环缓冲区

时间:2009-10-17 20:29:05

标签: javascript data-structures circular-buffer

有没有人在JavaScript中实现了循环缓冲区?如果没有指针,你会怎么做?

20 个答案:

答案 0 :(得分:30)

奇怪的共同发病率,我今天刚刚写了一篇!我不知道你的要求究竟是什么,但这可能有用。

它呈现的界面就像一个无限长度的数组,但“忘记”旧项目:

// Circular buffer storage. Externally-apparent 'length' increases indefinitely
// while any items with indexes below length-n will be forgotten (undefined
// will be returned if you try to get them, trying to set is an exception).
// n represents the initial length of the array, not a maximum
function CircularBuffer(n) {
    this._array= new Array(n);
    this.length= 0;
}
CircularBuffer.prototype.toString= function() {
    return '[object CircularBuffer('+this._array.length+') length '+this.length+']';
};
CircularBuffer.prototype.get= function(i) {
    if (i<0 || i<this.length-this._array.length)
        return undefined;
    return this._array[i%this._array.length];
};
CircularBuffer.prototype.set= function(i, v) {
    if (i<0 || i<this.length-this._array.length)
        throw CircularBuffer.IndexError;
    while (i>this.length) {
        this._array[this.length%this._array.length]= undefined;
        this.length++;
    }
    this._array[i%this._array.length]= v;
    if (i==this.length)
        this.length++;
};
CircularBuffer.IndexError= {};

答案 1 :(得分:19)

var createRingBuffer = function(length){

  var pointer = 0, buffer = []; 

  return {
    get  : function(key){return buffer[key];},
    push : function(item){
      buffer[pointer] = item;
      pointer = (length + pointer +1) % length;
    }
  };
};

更新:如果你只用数字填充缓冲区,这里有一些衬里插件:

min  : function(){return Math.min.apply(Math, buffer);},
sum  : function(){return buffer.reduce(function(a, b){ return a + b; }, 0);},

答案 2 :(得分:6)

和其他许多人一样,我喜欢noiv's solution,但我想要一个更好的API:

var createRingBuffer = function(length){
  /* https://stackoverflow.com/a/4774081 */
  var pointer = 0, buffer = []; 

  return {
    get  : function(key){
        if (key < 0){
            return buffer[pointer+key];
        } else if (key === false){
            return buffer[pointer - 1];
        } else{
            return buffer[key];
        }
    },
    push : function(item){
      buffer[pointer] = item;
      pointer = (pointer + 1) % length;
      return item;
    },
    prev : function(){
        var tmp_pointer = (pointer - 1) % length;
        if (buffer[tmp_pointer]){
            pointer = tmp_pointer;
            return buffer[pointer];
        }
    },
    next : function(){
        if (buffer[pointer]){
            pointer = (pointer + 1) % length;
            return buffer[pointer];
        }
    }
  };
};

原始改进:

  • get支持默认参数(将最后一项推送到缓冲区)
  • get支持否定索引(从右计算)
  • prev将缓冲区移回一个并返回其中的内容(如弹出而不删除)
  • next撤消prev(向前移动缓冲区并将其返回)

我用它来存储一个命令历史记录,然后我可以使用它的prevnext方法在应用程序中翻转这些方法,当它们无处可去时,很好地返回undefined。

答案 3 :(得分:4)

这是你可以使用的代码的快速模型(它可能不起作用并且有bug,但它显示了它可以完成的方式):

var CircularQueueItem = function(value, next, back) {
    this.next = next;
    this.value = value;
    this.back = back;
    return this;
};

var CircularQueue = function(queueLength){
    /// <summary>Creates a circular queue of specified length</summary>
    /// <param name="queueLength" type="int">Length of the circular queue</type>
    this._current = new CircularQueueItem(undefined, undefined, undefined);
    var item = this._current;
    for(var i = 0; i < queueLength - 1; i++)
    {
        item.next = new CircularQueueItem(undefined, undefined, item);
        item = item.next;
    }
    item.next = this._current;
    this._current.back = item;
}

CircularQueue.prototype.push = function(value){
    /// <summary>Pushes a value/object into the circular queue</summary>
    /// <param name="value">Any value/object that should be stored into the queue</param>
    this._current.value = value;
    this._current = this._current.next;
};

CircularQueue.prototype.pop = function(){
    /// <summary>Gets the last pushed value/object from the circular queue</summary>
    /// <returns>Returns the last pushed value/object from the circular queue</returns>
    this._current = this._current.back;
    return this._current.value;
};

使用这个对象就像:

var queue = new CircularQueue(10); // a circular queue with 10 items
queue.push(10);
queue.push(20);
alert(queue.pop());
alert(queue.pop());

你当然可以使用数组实现它,并使用一个内部使用数组的类,并保留当前项索引的值并移动它。

答案 4 :(得分:3)

我个人使用Trevor Norris的实现,你可以在这里找到: https://github.com/trevnorris/cbuffer

我很满意: - )

答案 5 :(得分:2)

短而甜蜜:

// IMPLEMENTATION
function CircularArray(maxLength) {
  this.maxLength = maxLength;
}

CircularArray.prototype = Object.create(Array.prototype);

CircularArray.prototype.push = function(element) {
  Array.prototype.push.call(this, element);
  while (this.length > this.maxLength) {
    this.shift();
  }
}

// USAGE
var ca = new CircularArray(2);
var i;

for (i = 0; i < 100; i++) {
  ca.push(i);
}

console.log(ca[0]);
console.log(ca[1]);
console.log("Length: " + ca.length);

输出:

98
99
Length: 2

答案 6 :(得分:1)

我真的很喜欢noiv11 solved this,为了我的需要,我添加了一个额外的属性'buffer'来返回缓冲区:

var createRingBuffer = function(length){

  var pointer = 0, buffer = []; 

  return {
    get  : function(key){return buffer[key];},
    push : function(item){
      buffer[pointer] = item;
      pointer = (length + pointer +1) % length;
    },
    buffer : buffer
  };
};

// sample use
var rbuffer = createRingBuffer(3);
rbuffer.push('a');
rbuffer.push('b');
rbuffer.push('c');
alert(rbuffer.buffer.toString());
rbuffer.push('d');
alert(rbuffer.buffer.toString());
var el = rbuffer.get(0);
alert(el);

答案 7 :(得分:1)

我无法让Robert Koritnik的代码工作,因此我将其编辑为以下似乎有用的代码:

    var CircularQueueItem = function (value, next, back) {
        this.next = next;
        this.value = value;
        this.back = back;
        return this;
    };

    var CircularQueue = function (queueLength) {
        /// <summary>Creates a circular queue of specified length</summary>
        /// <param name="queueLength" type="int">Length of the circular queue</type>
        this._current = new CircularQueueItem(undefined, undefined, undefined);
        var item = this._current;
        for (var i = 0; i < queueLength - 1; i++) {
            item.next = new CircularQueueItem(undefined, undefined, item);
            item = item.next;
        }
        item.next = this._current;
        this._current.back = item;

        this.push = function (value) {
            /// <summary>Pushes a value/object into the circular queue</summary>
            /// <param name="value">Any value/object that should be stored into the queue</param>
            this._current.value = value;
            this._current = this._current.next;
        };
        this.pop = function () {
            /// <summary>Gets the last pushed value/object from the circular queue</summary>
            /// <returns>Returns the last pushed value/object from the circular queue</returns>
            this._current = this._current.back;
            return this._current.value;
        };
        return this;
    }

使用:

    var queue = new CircularQueue(3); // a circular queue with 3 items
    queue.push("a");
    queue.push("b");
    queue.push("c");
    queue.push("d");
    alert(queue.pop()); // d
    alert(queue.pop()); // c
    alert(queue.pop()); // b
    alert(queue.pop()); // d
    alert(queue.pop()); // c

答案 8 :(得分:1)

我们可以使用一些内置的数组函数来实现循环队列实现,而不是用JavaScript实现循环队列。

例如: 假设我们需要实现长度为4的循环队列。

var circular = new Array();
var maxLength = 4;
var addElementToQueue = function(element){
    if(circular.length == maxLength){
        circular.pop();
    }
    circular.unshift(element);
};
addElementToQueue(1);
addElementToQueue(2);
addElementToQueue(3);
addElementToQueue(4);

输出:

圆形 [4,3,2,1]

如果您尝试将另一个元素添加到此数组,例如:

addElementToQueue(5);

输出:

圆形 [5,4,3,2]

答案 9 :(得分:0)

感谢你的简单而有效solution。我还需要能够像PerS did那样访问缓冲区,但我希望按照添加顺序获取项目。所以这就是我最终的结果:

function buffer(capacity) {
    if (!(capacity > 0)) {
        throw new Error();
    }

    var pointer = 0, buffer = [];

    var publicObj = {
        get: function (key) {
            if (key === undefined) {
                // return all items in the order they were added
                if (pointer == 0 || buffer.length < capacity) {
                    // the buffer as it is now is in order
                    return buffer;
                }
                // split and join the two parts so the result is in order
                return buffer.slice(pointer).concat(buffer.slice(0, pointer));
            }
            return buffer[key];
        },
        push: function (item) {
            buffer[pointer] = item;
            pointer = (capacity + pointer + 1) % capacity;
            // update public length field
            publicObj.length = buffer.length;
        },
        capacity: capacity,
        length: 0
    };

    return publicObj;
}

以下是测试套件:

QUnit.module("buffer");

QUnit.test("constructor", function () {
    QUnit.expect(4);

    QUnit.equal(buffer(1).capacity, 1, "minimum length of 1 is allowed");
    QUnit.equal(buffer(10).capacity, 10);

    QUnit.throws(
        function () {
            buffer(-1);
        },
        Error,
        "must throuw exception on negative length"
    );

    QUnit.throws(
        function () {
            buffer(0);
        },
        Error,
        "must throw exception on zero length"
    );
});

QUnit.test("push", function () {
    QUnit.expect(5);

    var b = buffer(5);
    QUnit.equal(b.length, 0);
    b.push("1");
    QUnit.equal(b.length, 1);
    b.push("2");
    b.push("3");
    b.push("4");
    b.push("5");
    QUnit.equal(b.length, 5);
    b.push("6");
    QUnit.equal(b.length, 5);
    b.push("7");
    b.push("8");
    QUnit.equal(b.length, 5);
});

QUnit.test("get(key)", function () {
    QUnit.expect(8);

    var b = buffer(3);
    QUnit.equal(b.get(0), undefined);
    b.push("a");
    QUnit.equal(b.get(0), "a");
    b.push("b");
    QUnit.equal(b.get(1), "b");
    b.push("c");
    QUnit.equal(b.get(2), "c");
    b.push("d");
    QUnit.equal(b.get(0), "d");

    b = buffer(1);
    b.push("1");
    QUnit.equal(b.get(0), "1");
    b.push("2");
    QUnit.equal(b.get(0), "2");
    QUnit.equal(b.length, 1);
});

QUnit.test("get()", function () {
    QUnit.expect(7);

    var b = buffer(3);
    QUnit.deepEqual(b.get(), []);
    b.push("a");
    QUnit.deepEqual(b.get(), ["a"]);
    b.push("b");
    QUnit.deepEqual(b.get(), ["a", "b"]);
    b.push("c");
    QUnit.deepEqual(b.get(), ["a", "b", "c"]);
    b.push("d");
    QUnit.deepEqual(b.get(), ["b", "c", "d"]);
    b.push("e");
    QUnit.deepEqual(b.get(), ["c", "d", "e"]);
    b.push("f");
    QUnit.deepEqual(b.get(), ["d", "e", "f"]);
});

答案 10 :(得分:0)

一种方法是使用其他人建议的链表。另一种技术是使用一个简单的数组作为缓冲区,并通过索引进入该数组来跟踪读写位置。

答案 11 :(得分:0)

我认为你应该能够通过使用对象来做到这一点。像这样:

var link = function(next, value) {
    this.next = next;
    this.value = value;
};

var last = new link();
var second = link(last);
var first = link(second);
last.next = first;

现在,您只需将值存储在每个链接的value属性中。

答案 12 :(得分:0)

无耻的自我插件:

如果你正在寻找一个旋转的node.js缓冲区,我写了一个可以在这里找到的:http://npmjs.org/packages/pivot-buffer

目前缺少文档,但RotatingBuffer#push允许您将缓冲区附加到当前缓冲区,如果新长度大于构造函数中指定的长度,则旋转先前的数据。

答案 13 :(得分:0)

如果您现在Array.prototype.length是什么,这将非常简单:

function CircularBuffer(size) {
  Array.call(this,size); //superclass
  this.length = 0; //current index
  this.size = size; //buffer size
};

CircularBuffer.prototype = Object.create(Array.prototype);
CircularBuffer.prototype.constructor = CircularBuffer;
CircularBuffer.prototype.constructor.name = "CircularBuffer";

CircularBuffer.prototype.push = function push(elem){
  Array.prototype.push.call(this,elem);
  if (this.length >= this.size) this.length = 0;
  return this.length;
}

CircularBuffer.prototype.pop = function pop(){
  var r = this[this.length];
  if (this.length <= 0) this.length = this.size;  
  this.length--;
  return r;
}

答案 14 :(得分:0)

近10年后,使用JavaScript ES6给出了答案:

    class CircularBuffer {
      constructor(bufferLength) {
        this.buffer = [];
        this.pointer = 0;
        this.bufferLength = bufferLength;
      }
      
      push(element) {
        if(this.buffer.length === this.bufferLength) {
           this.buffer[this.pointer] = element;
        } else {
           this.buffer.push(element);
        }
        this.pointer = (this.pointer + 1) % this.bufferLength;
      }
    
      get(i) {
        return this.buffer[i];
      }
      
      //Gets the ith element before last one 
      getLast(i) {
        return this.buffer[this.pointer+this.bufferLength-1-i];
      }
    
    }

//To use it:

let circularBuffer = new CircularBuffer(3);
circularBuffer.push('a');
circularBuffer.push('b');
circularBuffer.push('c');
// should print a,b,c
console.log(`0 element: ${circularBuffer.get(0)}; 1 element: ${circularBuffer.get(1)}; 2 element: ${circularBuffer.get(2)};`);

console.log('Last element: '+circularBuffer.getLast(0)); // should print 'c'

circularBuffer.push('d');

// should print d,b,c
console.log(`0 element: ${circularBuffer.get(0)}; 1 element: ${circularBuffer.get(1)}; 2 element: ${circularBuffer.get(2)};`);

答案 15 :(得分:0)

我更喜欢简单的方法。这应该是三班轮的IMO。

类似

const makeRing = sz                   => ({ sz, buf: new Array(size) }),
      at       = ({sz, buf}, pos)     => buf[pos % sz],
      set      = ({sz, buf}, pos, to) => buf[pos % sz] = to;

那你就可以

const ring = makeRing(10);

ring.buf.fill(1);
set(ring, 35, 'TWO!');

console.log(ring.buf);
console.log(at(ring, 65));

答案 16 :(得分:0)

很多答案,但没有看到类似以下功能简单的方法……(ES6):

const circularAdd = maxSize => (queue, newItem) =>
  queue.concat([newItem]).slice(Math.max(0, queue.length + 1 - maxSize));

可用作还原剂。例如。在scan的可见流中。

// Suppose newItem$ is a simple new value emitter
const itemBuffer$ = newItem$.pipe(scan(circularAdd(100), []));
// itemBuffer$ will now emit arrays with max 100 items, where the new item is last

修改

我现在看不到这个特定问题的答案,因为它没有提供阅读位置...:)

答案 17 :(得分:0)

我没有进行任何性能检查,但是据我了解,顺序数组访问应该比链接列表更快。我还注意到,多个实现都遭受了基于ES3(至少)的原型过时(至少)的困扰,这使我大吃一惊。而且它们都不支持动态大小增加,即“增长”。因此,这就是我如何看待此实现。随时根据您的需求进行扩展:

export class Dequeue<T> {
    private buffer: T[];
    private head: number;
    private tail: number;
    private size: number;

    constructor(initialCapacity: number) {
        this.buffer = [];
        this.buffer.length = initialCapacity;
        this.head = this.tail = this.size = 0;
    }

    public enqueue(value: T): T {
        let next = this.head + 1;
        let buffer = this.buffer;
        let length = buffer.length;

        if (length <= next) {
            next -= length;
        }

        if (buffer.length <= this.size) {
            buffer.length += length;

            for (let index = next; index < length; index++) {
                buffer[index + length] = buffer[index];
            }
        }

        this.size++;
        buffer[this.head] = value;
        this.head = next;

        return value;
    }

    public dequeue(): T | undefined {
        if (this.size > 0) {
            this.size--;

            let buffer = this.buffer;
            let length = buffer.length;
            let value = buffer[this.tail];

            let next = this.tail + 1;

            if (length <= next) {
                next -= length;
            }

            this.tail = next;

            return value;
        } else {
            return undefined;
        }
    }

    public get length() {
        return this.size;
    }
}

为防止undefined在界面中传播,我建议使用以下版本:

export function Throw(message: string): never {
    throw new Error(message);
}

export class Dequeue<T> {
    private buffer: T[];
    private head: number;
    private tail: number;
    private size: number;

    constructor(initialCapacity: number) {
        this.buffer = [];
        this.buffer.length = initialCapacity;
        this.head = this.tail = this.size = 0;
    }

    public enqueue(value: T): T {
        let next = this.head + 1;
        let buffer = this.buffer;
        let length = buffer.length;

        if (length <= next) {
            next -= length;
        }

        if (buffer.length <= this.size) {
            buffer.length += length;

            for (let index = next; index < length; index++) {
                buffer[index + length] = buffer[index];
            }
        }

        this.size++;
        buffer[this.head] = value;
        this.head = next;

        return value;
    }

    public dequeue(defaultValueFactory: () => T = () => Throw('No elements to dequeue')): T {
        if (this.size > 0) {
            this.size--;

            let buffer = this.buffer;
            let length = buffer.length;
            let value = buffer[this.tail];

            let next = this.tail + 1;

            if (length <= next) {
                next -= length;
            }

            this.tail = next;

            return value;
        } else {
            return defaultValueFactory();
        }
    }

    public get length() {
        return this.size;
    }
}

答案 18 :(得分:0)

这是我的看法。具体来说,这是圆形/环形滑动缓冲区的非常简单的对象实现。

一点便笺。尽管人们称呼它类似的名字,例如“圆形”,“环”,“队列”,但值得一说,因为它们含义不同。

  1. 环形/圆形队列。您可以将元素添加到头部,然后从末尾进行裁剪。最小大小为0,最大大小为基础数组的大小。队列环绕基础数组。

  2. 同一件事,一个队列,FIFO,先进先出,但最大大小可变(不确定),并使用标准push()和unshift()数组方法实现。要添加元素,只需将它推入()到数组上,然后使用unshift()来消耗元素,就这样,它是非常标准的函数,不需要发明任何东西。

  3. 一个固定大小的滑动缓冲区,其中新元素添加到头部(右侧),该缓冲区向后滑动(左侧),最左边的多余元素自动丢失。从概念上说,它是一个滑动缓冲区,只是碰巧可以最有效地实现为圆形/环形。

这是(3)种的实现。这可以用作数据可视化窗口小部件的后端,并且主要用于此目的。实时监测的滑动线图。

对象:

function make_CRS_Buffer(size) {
    return {
        A:  [],
        Ai: 0,
        Asz:    size,
        add:    function(value) {
            this.A[ this.Ai ] = value;
            this.Ai = (this.Ai + 1) % this.Asz;
        },
        forall: function(callback) {
            var mAi = this.A.length < this.Asz ? 0 : this.Ai;
            for (var i = 0; i < this.A.length; i++) {
                callback(this.A[ (mAi + i) % this.Asz ]);
            }

        }
    };
}

用法:

var buff1 = make_CRS_Buffer(5);

buff1.add(cnt);

buff1.forall(value => {
    b1.innerHTML += value + " ";
});

还有一个完整的功能示例,其中两个缓冲区并行运行:

var b1 = document.getElementById("b1");
var b2 = document.getElementById("b2");

var cnt = 0;

var buff1 = make_CRS_Buffer(5);
var buff2 = make_CRS_Buffer(12);


function add() {
	buff1.add(cnt);
	buff2.add(cnt);
	cnt ++;
	
	b1.innerHTML = "";
	buff1.forall(value => {
		b1.innerHTML += value + " ";
	});
	
	b2.innerHTML = "";
	buff2.forall(value => {
		b2.innerHTML += value + " ";
	});
}

function make_CRS_Buffer(size) {
	return {
		A:	[],
		Ai:	0,
		Asz:	size,
		add:	function(value) {
			this.A[ this.Ai ] = value;
			this.Ai = (this.Ai + 1) % this.Asz;
		},
		forall:	function(callback) {
			var mAi = this.A.length < this.Asz ? 0 : this.Ai;
			for (var i = 0; i < this.A.length; i++) {
				callback(this.A[ (mAi + i) % this.Asz ]);
			}
		
		}
	};
}
<!DOCTYPE html>
<html>
<body>

<h1>Circular/Ring Sliding Buffer</h1>

<p><i>(c) 2020, Leonid Titov</i>

<div id="b1" style="
	background-color: hsl(0,0%,80%);
	padding: 5px;
">empty</div>

<div id="b2" style="
	background-color: hsl(0,0%,80%);
	padding: 5px;
">empty</div>

<br>
<button onclick="add()">Add one more</button>

</body>
</html>

希望它会有用。

答案 19 :(得分:0)

我建议使用 TypeScript 循环数组实现:https://gist.github.com/jerome-benoit/c251bdf872473d1f86ea3a8b90063c90。 精简,API 与标准数组对象相同。