sort

摘要

直接对数组的元素进行排序.

Array 的方法
实现方式: JavaScript 1.1, NES 2.0

JavaScript 1.2: 修改过的行为.

ECMA 版本: ECMA-262

语法

array.sort(compareFunction);

参数

compareFunction 
用来指定按某种顺序进行排列的函数. 如果省略, the array is sorted lexicographically (in dictionary order) according to the string conversion of each element.

Description

If compareFunction is not supplied, elements are sorted by converting them to strings and comparing strings in lexicographic ("dictionary" or "telephone book," not numerical) order. For example, "80" comes before "9" in lexicographic order, but in a numeric sort 9 comes before 80.

If compareFunction is supplied, the array elements are sorted according to the return value of the compare function. If a and b are two elements being compared, then:

  • If compareFunction(a, b) is less than 0, sort a to a lower index than b.
  • If compareFunction(a, b) returns 0, leave a and b unchanged with respect to each other, but sorted with respect to all different elements. Note: the ECMAscript standard does not guarantee this behaviour, and thus not all browsers (e.g. Mozilla versions dating back to at least 2003) respect this.
  • If compareFunction(a, b) is greater than 0, sort b to a lower index than a.

So, the compare function has the following form:

function compare(a, b)
{
  if (a is less than b by some ordering criterion)
     return -1;
  if (a is greater than b by the ordering criterion)
     return 1;
  // a must be equal to b
  return 0;
}

To compare numbers instead of strings, the compare function can simply subtract b from a:

function compareNumbers(a, b)
{
  return a - b;
}

Some implementations of JavaScript implement a stable sort: the index partial order of a and b does not change if a and b are equal. If a's index was less than b's before sorting, it will be after sorting, no matter how a and b move due to sorting.

Sort is stable in SpiderMonkey and all Mozilla-based browsers starting with Gecko 1.9 (see bug 224128).

The behavior of the sort method changed between JavaScript 1.1 and JavaScript 1.2.

In JavaScript 1.1, on some platforms, the sort method does not work. This method works on all platforms for JavaScript 1.2.

In JavaScript 1.2, this method no longer converts undefined elements to null; instead it sorts them to the high end of the array. For example, assume you have this script:

var a = [];
a[0] = "Ant";
a[5] = "Zebra";

// assumes a print function is defined
function writeArray(x)
{
  for (i = 0; i < x.length; i++)
  {
    print(x[i]);
    if (i < x.length-1)
      print(", ");
  }
}

writeArray(a);
a.sort();
print("\n");
writeArray(a);

In JavaScript 1.1, JavaScript prints:

ant, null, null, null, null, zebra
ant, null, null, null, null, zebra

In JavaScript 1.2, JavaScript prints:

ant, undefined, undefined, undefined, undefined, zebra
ant, zebra, undefined, undefined, undefined, undefined

Examples

Example: Creating, displaying, and sorting an array

The following example creates four arrays and displays the original array, then the sorted arrays. The numeric arrays are sorted without, then with, a compare function.

var stringArray = ["Blue", "Humpback", "Beluga"];
var numericStringArray = ["80", "9", "700"];
var numberArray = [40, 1, 5, 200];
var mixedNumericArray = ["80", "9", "700", 40, 1, 5, 200];

function compareNumbers(a, b)
{
  return a - b;
}

// again, assumes a print function is defined
print("stringArray: " + stringArray.join() +"\n");
print("Sorted: " + stringArray.sort() +"\n\n");

print("numberArray: " + numberArray.join() +"\n");
print("Sorted without a compare function: " + numberArray.sort() +"\n");
print("Sorted with compareNumbers: " + numberArray.sort(compareNumbers) +"\n\n");

print("numericStringArray: " + numericStringArray.join() +"\n");
print("Sorted without a compare function: " + numericStringArray.sort() +"\n");
print("Sorted with compareNumbers: " + numericStringArray.sort(compareNumbers) +"\n\n");
print("mixedNumericArray: " + mixedNumericArray.join() +"\n");
print("Sorted without a compare function: " + mixedNumericArray.sort() +"\n");
print("Sorted with compareNumbers: " + mixedNumericArray.sort(compareNumbers) +"\n\n");

This example produces the following output. As the output shows, when a compare function is used, numbers sort correctly whether they are numbers or numeric strings.

stringArray: Blue,Humpback,Beluga
Sorted: Beluga,Blue,Humpback

numberArray: 40,1,5,200
Sorted without a compare function: 1,200,40,5
Sorted with compareNumbers: 1,5,40,200

numericStringArray: 80,9,700
Sorted without a compare function: 700,80,9
Sorted with compareNumbers: 9,80,700

mixedNumericArray: 80,9,700,40,1,5,200
Sorted without a compare function: 1,200,40,5,700,80,9
Sorted with compareNumbers: 1,5,9,40,80,200,700

See Also

join, reverse

Document Tags and Contributors

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