【JavaScript 学习--02】--排序问题（正序和逆序）

在JS里常常用到排序(包括正序和逆序)，特记录下

1.正序

原始数据为：

var test_order = [{order:5, name:"tl1"},{name:"tl2"},{order:4, name:"tl3"},{order:1, name:"tl4"}]

1.1 利用JS的sort（）正序排序

test_order.sort(function (a,b) {
console.log("a=" + a.name+";b="+ b.name);
return (a.order||0) - (b.order||0);
});

执行结果是：

[{name: "tl2"},{order: 1, name: "tl4"},{order: 4, name: "tl3"},{order: 5, name: "tl1"}]

==============

实际执行过程是如下这样：

a=tl1;b=tl2
a=tl1;b=tl3
a=tl2;b=tl3
a=tl1;b=tl4
a=tl3;b=tl4
a=tl2;b=tl4

—————————–深入理解sort

关于sort()的详细内容可以参考：http://www.w3schools.com/jsref/jsref_sort.asp



Example

Sort numbers in an array in ascending(up) order:

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a-b});

The result of points will be:

1,5,10,25,40,100

Sort numbers in an array in descending(down) order:

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b-a});

The result of points will be:

100,40,25,10,5,1

1.2 Lodash 的sortBy 正序排序

Lodash官方网站可以查阅：Lodash docs

例子：

var myArray = [ 3, 4, 2, 9, 4, 2 ];

_.sortBy(myArray);
// → [ 2, 2, 3, 4, 4, 9 ]

_(myArray).sortBy().take(3).value();
// → [ 2, 2, 3 ]

var users = [
{ 'user': 'fred',   'age': 48 },
{ 'user': 'barney', 'age': 36 },
{ 'user': 'fred',   'age': 40 },
{ 'user': 'barney', 'age': 34 }
];

_.sortBy(users, [function(o) { return o.user; }]);
// => objects for [['barney', 36], ['barney', 34], ['fred', 48], ['fred', 40]]

_.sortBy(users, ['user', 'age']);
// => objects for [['barney', 34], ['barney', 36], ['fred', 40], ['fred', 48]]

2.逆序

2.1 JS原生态的sort进行逆序排序

可以将正序里面的匿名函数返回值前加个负号，或者用后者减去前者也可以实现。比如：

test_order.sort(function (a,b) {
return -(a.order||0) - (b.order||0);
});

//====>等价于
test_order.sort(function (a,b) {
return (b.order||0) - (a.order||0);
});

2.2 Lodash库的orderBy进行逆序排序

As of lodash 3.5.0 you can use sortByOrder (renamed orderBy in v4.3.0):

var data = _.sortByOrder(array_of_objects, ['type','name'], [true, false]);

Since version 3.10.0 you can even use standard semantics for ordering (asc, desc):

var data = _.sortByOrder(array_of_objects, ['type','name'], ['asc', 'desc']);

In version 4 of lodash this method has been renamed orderBy:

var data = _.orderBy(array_of_objects, ['type','name'], ['asc', 'desc']);