PHP array definition, variable destruction and one-dimensional array sorting

This article first introduces the array definition and destruction of arrays in PHP, and then uses an example to illustrate the sorting method of one-dimensional data. Friends in need can refer to it. I hope it will be useful to everyone.

Definition of PHP array

The code is as follows

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代码如下	复制代码
…… $array = array('one','two','three'); var_dump($array); ……

……

$array = array('one','two','three');

var_dump($array);

代码如下	复制代码
array(3) { [0]=> string(3) "one" [1]=> string(3) "two" [2]=> string(5) "three" }

…

In the first line of this code snippet, a one-dimensional array $array is defined. In the second line, we format and output the array. The result is like this:

The code is as follows

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array(3) { [0]=>

代码如下	复制代码
…… $array = array('one',”hello”=>'two','three'); var_dump($array);

string(3) "one"

[1]=>

string(3) "two"

代码如下	复制代码
array(3) { [0]=> string(3) "one" ["hello"]=> string(3) "two" [1]=> string(5) "three" }

[2]=>

string(5) "three"

}

Now brothers explain this output result. First, the first line of the output result of this array,

代码如下	复制代码
…… $array = array(-5=>'one',"hello"=>'two','three'); var_dump($array); ……

array(3) tells us that this is an array with three elements, First, element 0 is a string of length 3 (string(3))... Due to space constraints, I won’t talk about the remaining two. Hoho…, what does this mean? This shows that in PHP, if we do not specify a subscript for the array, then it will make a subscript for us from scratch on its own initiative - that is, the key name in the PHP array; look at the following example:

The code is as follows	Copy code
…… $array = array('one',"hello"=>'two','three'); var_dump($array);

...This time when we defined the array, we specified the subscript for the second element (from now on, it will be called the key name in this article, the subscript is a bit ambiguous!), and the second element specified Key name (hello), let’s take a look at the output:

The code is as follows	Copy code
array(3) { [0]=> string(3) "one" ["hello"]=> string(3) "two" [1]=> string(5) "three" }

I think you have also seen a very smart phenomenon like me. The key name of the first element is still 0 - we can understand this because we did not specify it, and the PHP array must have a key name, PHP We created a key name from scratch on our own initiative; for the second element, we specified the key name, and PHP respected our opinion and used this key name; the complicated thing is in the third element, The third element looks very simple. We did not specify a key name. PHP automatically adds 1 to the maximum integer key name as the key name. But have you ever thought about it, if we change the key name of the first element to "-5" and the key name of the second element remains unchanged, what will be the result? Let’s wait and see:

The code is as follows	Copy code
…… $array = array(-5=>'one',"hello"=>'two','three'); var_dump($array); ……

If you take it for granted that the key name of the third element should be -4, then I tell you that this idea was correct before PHP4.3.0, but it was wrong after that, and now it is after PHP4.3.0 Version you will see the following results:

The code is as follows

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代码如下	复制代码
array(3) { [-5]=> string(3) "one" ["hello"]=> string(3) "two" [0]=> string(5) "three" }

array(3) {

[-5]=>

string(3) "one"

["hello"]=>
string(3) "two"
[0]=>

string(5) "three"

}

Yes, the third element starts from 0, that is, no matter how small your negative number is, if the next element is asked to define the key name by PHP, then it will start from 0 - remember this place says What's interesting is that if the largest key name among the existing keys is still a negative number, no matter how small the negative number is, PHP will start the next key name from zero.

Destruction of PHP arrays is as simple as destroying other variables.
Destroy the entire array: unset($array)

Destroy an element in the array: unset($array[-5])

代码如下

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$a = array("a"=>1,2);
sort($a);
var_dump($a);

rsort($a);
var_dump($a);
?>

看一下第一个输出结果，第一个输出：
array(2) {
[0]=>
int(1)
[1]=>
int(2)
}
第二个输出：
array(2) {
[0]=>
int(5)
[1]=>
int(4)
}

Whether in real life or in the programming world, order is always important - I can’t imagine what a world without order would be like! PHP arrays are no exception. PHP provides four sets of functions for sorting PHP arrays. The first three are for one-dimensional arrays. Let's talk about these three first. The fourth sorting of multi-dimensional arrays will be discussed in the next article. That one is a bit complicated.

The first group: sort and rsort, sort according to the order asc and reverse order desc of the PHP array key value, while destroying the index relationship of the original array - in fact, re-establishing a numerical index starting from 0 after deleting the index. Take a look at the routine:

代码如下	复制代码
array(2) { ["a"]=> int(1) [0]=> int(2) } array(2) { [0]=> int(2) ["a"]=> int(1) }

The code is as follows	Copy code
$a = array("a"=>1,2); sort($a); var_dump($a); rsort($a); var_dump($a); ?> Look at the first output result, the first output: array(2) { [0]=> int(1) [1]=> int(2) } Second output: array(2) { [0]=> int(5) [1]=> int(4) }

Found that there is no index a we originally defined, where is it? Where did it go? It can be said with certainty that they were ruthlessly deleted by them. If you don’t care about the original index relationship, you can use them! The second set of functions: asort and arsort. These two functions are more powerful. As long as they can retain the original index relationship of the array, replace the sort and rsort in the above example with these two functions. See Running result:

The code is as follows	Copy code
array(2) { ["a"]=> int(1) [0]=> int(2) } array(2) { [0]=> int(2) ["a"]=> int(1) }

这个一看就明白的，不用说了吧！

第三组PHP数组排序函数：krsort 和 ksort 这两个不同于以上两组，这两函数是对键名进行排序的，大家可以把上例的函数替换成这两个，看看具体运行结果，这里也不说了，不然这个文章写的就太长了，怕有些兄弟没有耐心看到本文的重点，虽然重点就在下边！

通过自定义函数对PHP数组进行排序，有三个函数分别是：
uasort 通过自定义函数对PHP数组的键值进行排序，并且保留原来的索引关系。
uksort 通过自定义函数对PHP数组的键名进行排序，并且保留原来的索引关系。
usort通过自定义函数对PHP数组的键值进行排序，并且删除原来的索引关系，从零开始建立新的索引。

这个地方当然需要一个例子：

输出结果：
array(4) {
[0]=>
int(1)
[3]=>
int(5)
[1]=>
int(4)
[2]=>
int(3)
}

，呵呵……是不是比不排序还乱呢？我们这里只是演示了使用的方法而已，具体你用到的时候自己搞吧！你要是不对这些数值进行操作之后再比较，例如我们这里：
$a+=1;
$b+=3;//改变这些值之后进行比较

在PHP手册中，一共定义了74个数组函数，涵盖了PHP数组的定义，赋值，排序，数值操作，比较，以及对数组的键名，键值反转……等等我们几乎能够想到的所有功能。有需要的同学可以去参考一下啊