underscorejs-sample学习

2.22 sample

2.22.1 语法:

_.sample(list, [n])

2.22.2 说明:

从list中产生一个随机样本。传参n后返回n个随机元素，各元素不重复。

2.22.3 代码示例:

示例一：从list中随机产生一个样本

var sample;

//数组
sample = _.sample([1, 2, 3, 4, 5]);
console.log(sample); //may be => Number 3

//对象
sample = _.sample({a:1, b:2, c:3, d:4, e: 5}); 
console.log(sample); //may be => Number 2

//字符串
sample = _.sample('12345'); 
console.log(sample); //may be => String 5

//arguments
(function(){
sample = _.sample(arguments); 
console.log(sample); //may be => Number 1
}(1, 2, 3, 4, 5));

示例二：传递参数n

var sample;

//数组
sample = _.sample([1, 2, 3, 4, 5], 3);
console.log(sample); //may be => [4, 2, 3]

//对象
sample = _.sample({a:1, b:2, c:3, d:4, e: 5}, 3); 
console.log(sample); //may be => [1, 2, 4]

//字符串
sample = _.sample('12345', 3); 
console.log(sample); //may be => ["5", "1", "4"]

//arguments
(function(){
sample = _.sample(arguments, 3); 
console.log(sample);  //may be => [3, 2, 4]
}(1, 2, 3, 4, 5));

传递n后，返回的是数组。

2.22.3 传递参数n的变化

var list = [1, 2, 3, 4, 5];
var sample;

sample = _.sample(list, -1);
console.log(sample); //=> []

sample = _.sample(list, 0);
console.log(sample); //=> []

//传1返回的也是数组
sample = _.sample(list, 1);
console.log(sample); //may be => [1]

sample = _.sample(list, 3);
console.log(sample); //may be => [1, 2, 4]

sample = _.sample(list, 5);
console.log(sample); //may be => [5, 3, 1, 2, 4]

sample = _.sample(list, 10);
console.log(sample); //may be => [2, 4, 5, 1, 3]

• 传递了参数n返回的都是数组
• n <= 0 返回空数组
• n > 0 && n < list.length 返回的数组长度为n
• n >= list.length返回的数组长度为list.length

2.22.4 产生的一个样本内，各元素不会重复

var list = [1, 2, 3, 4, 5];
var sample;

_(3).times(function(){
    sample = _.sample(list, 5);
    console.log(sample);
});

2.22.5 非集合情况都返回undefined

console.log(_.sample([])); //=> undefined
console.log(_.sample(1)); //=> undefined
console.log(_.sample(null)); //=> undefined
console.log(_.sample(undefined)); //=> undefined
console.log(_.sample(NaN)); //=> undefined

2.22.6 简单的random，元素的值可能重复

var list = ['a', 'b', 'c', 'd'];
var sample = [];

for(var i = 0; i < list.length; i++) {
    var n = Math.floor(Math.random() * list.length);
    sample.push(list[n]);
}
console.log(sample); //maybe => ["c", "d", "c", "a"]