How to use the sort() method in javascript

In JavaScript, the sort() method is used for array sorting. This method can sort array elements according to certain conditions. The syntax format is "arrayObject.sort(sortby)". If the sort() method is called without passing arguments, the elements in the array are sorted alphabetically.

The operating environment of this tutorial: Windows 7 system, JavaScript version 1.8.5, Dell G3 computer.

Use sort() to sort the array

The sort() method can sort the array elements according to certain conditions. If the sort() method is called without passing arguments, the elements in the array are sorted alphabetically.

var a = ["a","e","d","b","c"];  //定义数组
a.sort();  //按字母顺序对元素进行排序
console.log(a);  //返回数组[a,b,c,d,e]

When using the sort() method, you should pay attention to the following issues.

1) The so-called alphabetical order is actually arranged according to the order of letters in the character encoding table. Each character has a unique number in the character table.

2) If the element is not a string, the sort() method attempts to convert the array elements into a string for comparison.

3) The sort() method will perform a bit-by-bit comparison based on element values, rather than sorting based on the number of strings.

var a = ["aba","baa","aab"];  定义数组
a.sort();  //按字母顺序对元素进行排序
console.log(a);  //返回数组[aab,aba,baa]

When sorting, first compare the first character of each element. If the first character is the same, compare the second character, and so on.

4) In any case, undefined elements in the array are sorted at the end.

5) The sort() method performs sorting operations on the original array and does not create a new array.

The sort() method not only sorts alphabetically, but can also perform operations according to other orders. In this case, the method must be provided with a function parameter that compares the two values ​​and returns a number that describes the relative order of the two values. The sort function should have two parameters, a and b, and its return value is as follows.

• If a is less than b according to the custom criteria, a should appear before b in the sorted array, then a value less than 0 is returned.

• If a is equal to b, return 0.

• If a is greater than b, return a value greater than 0.

Example 1

In the following example, the size of each element in the array will be compared according to the sorting function, and sorted from small to large Sorting is performed sequentially.

function f(a,b) {  //排序函数
    return (a - b);  //返回比较参数
}
var a = [3,1,2,4,5,7,6,8,0,9];  //定义数组
a.sort(f);  //根据数字大小由小到大进行排序
console.log(a);  //返回数组[0,1,2,3,4,5,6,4,7,8,9]

If executed in order from large to small, just invert the return value. The code is as follows:

function f(a,b) {  //排序函数
    return -(a - b);  //取反并返回比较参数
}
var a = [3,1,2,4,5,7,6,8,0,9];  //定义数组
a.sort(f);  //根据数字大小由小到大进行排序
console.log(a);  //返回数组[9,8,7,6,5,4,3,2,1,0]

Example 2

Arrange the array according to the odd and even properties.

sort() is more flexible in usage, mainly for function sorting and comparison. For example, if you sort an array according to odd and even numbers, you only need to determine whether the two parameters in the sequence function are odd and even numbers, and determine the sort order.

function f(a, b) {  //排序函数
    var a = a % 2;  //获取参数a的奇偶性
    var b = b % 2;  //获取参数b的奇偶性
    if (a == 0) return 1;  //如果参数a为偶数，则排在左边
    if (b == 0) return -1;  //如果参数b为偶数，则排在右边
}
var a = [3,1,2,4,5,7,6,8,0,9];  //定义数组
a.sort(f);  //根据数字大小由大到小进行排序
console.log(a);  //返回数组[3,1,5,7,9,0,8,6,4,2]

sort() method passes each element value to the sorting function when calling the sorting function. If the element value is an even number, its position will be kept unchanged; if the element value is an odd number, the parameter a will be exchanged. and the display order of b, thereby performing odd-even sorting of all elements in the array. If you want even numbers to be sorted first and odd numbers to be sorted behind, you only need to get the return value. The sorting function is as follows.

function f(a, b) {
    var a = a % 2;
    var b = b % 2;
    if (a == 0) return -1;
    if (b == 0) return 1;
}

Example 3

Sort strings case-insensitively.

Under normal circumstances, sorting strings is case-sensitive, because the order of each uppercase letter and lowercase letter in the character encoding table is different, and uppercase letters are larger than lowercase letters.

var a = ["aB", "Ab", "Ba", "bA"];  //定义数组
a.sort();  //默认方法排序
console.log(a);  //返回数组["Ab", "Ba", "aB", "bA"]

Capital letters are always arranged on the left. If you want lowercase letters to always be arranged on the left, you can design:

function f(a ,b) {
    return (a < b);
}
var a = ["aB", "Ab", "Ba", "bA"];  //定义数组
a.sort();  //默认方法排序
console.log(a);  //返回数组["Ab", "Ba", "aB", "bA"]

When comparing the sizes of letters, JavaScript is based on the character encoding size. Determined, when it is true, it returns 1; when it is false, it returns -1.

If you do not want to be case-sensitive, and uppercase letters and lowercase letters are arranged in the same order, you can design:

function f(a, b) {
    var a = a.toLowerCase;
    var b = b.toLowerCase; 
    if (a < b) {
        return 1;
    }
    else {
        return -1;
    }
}
var a = ["aB", "Ab", "Ba", "bA"];  //定义数组
a.sort();  //默认方法排序
console.log(a);  //返回数组["aB", "Ab", "Ba", "bA"]

If you want to adjust the sorting order, just set the return value to be inverted.

Example 4

Display floating point numbers and integers separately.

function f(a, b) {  //排序函数
    if (a > Math.floor(a)) return 1;  //如果a是浮点数，则调换位置
    if (b > Math.floor(b)) return -1;  //如果b是浮点数，则调换位置
}
var a = [3.5555, 1.23456, 3, 2.11111, 5, 7, 3];  //定义数组
a.sort(f);  //进行筛选
console.log(a);  //返回数组[3,5,7,3,2.11111,1.23456,3.55555]

If you want to adjust the sort order, just set the return value to be inverted.

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