Processing of php arrays (Array function)

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What is PHP Array?

An array is a collection of data that organizes a series of data to form an operable whole. Arrays in PHP are complex but more flexible than arrays in many other high-level languages.

Array An array is an ordered set of variables, where each value is called an element. Each element is distinguished by a special identifier called a key (also called a subscript).

Each entity in the array contains two items, namely key and value. The corresponding array elements can be obtained by key value. These keys can be numeric keys or association keys. If a variable is a container that stores a single value, then an array is a container that stores multiple values.

PHP arrays are more flexible than arrays in other high-level languages. They not only support index arrays with numbers as keys, but also support associative arrays with strings or a mixture of strings and numbers as keys. In other high-level languages, such as Java or C, only numerically indexed arrays are supported.

The structure of the PHP array is as shown below:

In PHP, there are three array types:

• Index array: an array with a numeric index

• Associative array: an array with a specified key

• Multidimensional array: contains one or more An array of arrays

Recommended video tutorial:

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Recommended study manual: "php Complete Self-Study Manual"

PHP Array Use

PHP Array Definition

[1,  5,  1.1,  'abc'  true,  false] //可以存储任何数据，此时为'默认下标'，

[2=>1,  5=>5,  3=>1.1,  7=>'abc'  0=>true]//下标可以任意设定（无需顺序，无需连续）

[2=>1,  5,  1=>1.1,  'abc'  0=>true]//可以加下标，也可以不加（默认下标）,下标分别是：2,3,1,4,0

//默认下标规则：前面已经用过的最大数字下标+1

[2=>1,  'dd'=>5,  1=>1.1,  'abc'  0=>true]//混合下标，同样遵循默认下标规则

[-2=>1,  'dd'=>5,  1.1,  'abc'  true]; //负数下标不算在整数下标中，而只当作字符下标

//则最好3项的下标是：0, 1, 2

[2.7=>1,  'dd'=>5,  1=>1.1,  'abc'  0=>true]//浮点数下标为自动转换为整数，且直接抹掉小数

['2.7' =>1,  'dd'=>5,  '11'=>1.1,  'abc'  true]//纯数字字符串下标，当作数字看待，

//则此时下标为：2, 'dd', 11, 12, 13

[2=>1,  'dd'=>5,  true=>1.1,  'abc'  false=>true]//布尔值当下标，则true为1，false为0；

[2=>1,  'dd'=>5,  2=>1.1,  'abc'  true]//如果下标跟前面的重复，则单纯覆盖前面同名下标的值

Associative array

$array = [
    'name' => 'zhaosi',
    'age' => 20,
    'sex' => '女'
];

Multidimensional array

$array = [
    [
        'name' => 'xiaoming',
        'age' => 17,
        'sex' => '男'
    ],
    [
        'name' => 'wanghua',
        'age' => 16,
        'sex' => '女'
    ],
    [
        'name' => 'zhaosi',
        'age' => 20,
        'sex' => '女'
    ],
    [
        'name' => 'zhangsan',
        'age' => 22,
        'sex' => '男'
    ],
    [
        'name' => 'wangli',
        'age' => 12,
        'sex' => '女'
    ],
    [
        'name' => 'zhuhua',
        'age' => 14,
        'sex' => '男'
    ]
];

Array traversal

$array = [
    [
        'name' => 'xiaoming',
        'age' => 17,
        'sex' => '男'
    ],
    [
        'name' => 'wanghua',
        'age' => 16,
        'sex' => '女'
    ],
    [
        'name' => 'zhaosi',
        'age' => 20,
        'sex' => '女'
    ],
    [
        'name' => 'zhangsan',
        'age' => 22,
        'sex' => '男'
    ],
    [
        'name' => 'wangli',
        'age' => 12,
        'sex' => '女'
    ],
    [
        'name' => 'zhuhua',
        'age' => 14,
        'sex' => '男'
    ]
];



foreach ($array as $key => $value) {
    echo $value['name'];
    echo $value['age'];
    echo $value['sex'];
}

Output result

xiaoming
17
男
wanghua
16
女
zhaosi
20
女
zhangsan
22
男
wangli
12
女
zhuhua
14
男

Commonly used PHP array functions

1. The count() function is used to count the number of elements in the array or the number of attributes in the object. Number

int count(mixed var[,int mode])

The first parameter is required, passing a calculated array or object. The second parameter is optional and specifies whether the mode of the function recursively calculates the number of elements in the array in the multi-dimensional array. The possible values ​​are 0 or 1. 0 is the default value and multi-dimensional arrays are not detected. If it is 1, multi-dimensional arrays are detected.

Example:

$a = array(
    "a",
    "b",
    "c",
    "d"
);
echo count($a); //输出个数4
$b = array(
    "a" => array(
        1,
        2,
        3
    ) ,
    "b" => array(
        4,
        5,
        6
    )
);
echo count($b, 1); //输出 8
echo count($b); //输出 2y([b]=>2 [d]=>4)

2. The array_count_values() function is used to count the number of occurrences of all values ​​in the array. This function has only one parameter

array array_count_values(array input)

parameter Specifies that an array is input and an array is returned. The key name of its element is the value of the original array, and the key value is the number of times the value appears in the original array.

Example:

$array=array(1,"a",1,"b","a");
$newarray=array_count_values($array);
print_r($newarray);//输出array([1]=>2 [a]=>2 [b]=>1)

3 The array_unique() function is used to delete duplicate values ​​in the array and return a new array without duplicate values

array array_unique(array array)

The parameter needs to accept an array. When the values ​​​​of several elements in the array are equal, only The first element is retained, other elements are deleted, and the key names in the returned new array remain unchanged. array_unique() first sorts the values ​​as strings, then only retains the first encountered key name for each value, and then ignores it. All following key names

Example:

$a=array("a"=>1,"b"=>2,"c"=>1);
print_r(array_unique($a));//输出 array([a]=>1 [b]=>2)

4. The array_filter() function uses the callback function to filter the elements in the array and returns the array filtered by the user-defined function

array array_filter(array input [,callback callback])

Parameters: The first parameter is required and requires input of a filtered array. The second parameter is optional. Pass in the user-defined function name in the form of a string. If the custom filter function returns If true, the current value of the operated array will be included in the returned result array, and the result will be formed into a new array. If the original array is an associative array, the key name will remain unchanged.

Example:

function myFun($var) {
    if ($var % 2 == 0) {
        return true;
    }
}
$array = array(
    "a" => 1,
    "b" => 2,
    "c" => 3,
    "d" => 4
);
print_r($array, "myFun"); //输出 array([b]=>2 [d]=>4)

5. The array_walk() function applies callback function processing to each element in the array. If successful, it returns true, otherwise it returns false

bool array_walk( array &array,callback funcname [,mixed userdata])

The first parameter is required and requires the input of an array processed by the specified callback function. The second parameter is passed to the user-defined callback function and is used to operate the array passed to the first parameter

Example :

function myFunc1($value, $key) {
    echo "key=$key value=$value";
}
$a = ["a" => "lin1", "b" => "lin2", "c" => "lin3"];
array_walk($a, "myFunc1");
function myFunc2($value, $key, $str) {
    echo "$key $value";
}
array_walk($a, "myFunc2");
function myFunc3($value, $key) {
    $value = "lin.su";
}
array_walk($a, "myFunc3");
print_r($a); //$a 是一个引用数组

6. The array_map() function can process multiple arrays, apply the callback function to the elements of the given array, and return the array after the user-defined function is applied.

array array_map(callback callback,array arr1[,arry ....])

Example:

function myFunc($v1, $v2) {
    if ($v1 == $v2) {
        return "same";
    }
    return "different";
}
$a = [1, 2, 3];
$b = [1, 4, 3];
print_r(array_map("myFunc", $a, $b)); //输出 array([0]=>same [1]=>difference [2]=>same)
print_r(array_map(null, $a, $b));

Output:

array(
[0]=>array([0]=>1 [1]=>2 [2]=>3)
[1]=>array([0]=>1 [1]=>2 [2]=>3)
)

PHP Array Function

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