Summary of basic PHP array operations (recommended), summary of basic operations

Summary of basic PHP array operations (recommended), summary of basic operations

The concept of array

Array is a very important concept in PHP. We can think of an array as a collection of similar data. In fact, an array is an ordered graph.

PHP also provides over 70 built-in functions to operate on arrays.

Create array

Create an array using the array() language construct:

<&#63;php
$arr_age1 = array(18, 20, 25);
// 或者：
$arr_age2 = array("wang"=>18, "li"=>20, "zhang"=>25);
// 空数组：
$arr_age3 =array();
&#63;>

You can also use the array controller [] to create an array:

<&#63;php
$arr_age1[] = 18;
$arr_age1[] = 20;
$arr_age1[] = 25;
// 或者：
$arr_age2["wang"] = 18;
$arr_age2["li"] = 20;
$arr_age2["zhang"] = 25;
&#63;> 

Array key name and value

Array entities contain two items: key name and value.

In the following example of creating an array:

$arr_age1 = array(18, 20, 25); We allocate 3 array units (also called elements) to $arr_age1, whose values ​​are 18, 20 and 25 respectively. The system will automatically assign three numerical serial numbers to these three array units, which are 0, 1 and 2 respectively. That is, the complete structure of the $arr_age1 array is:

Array ( [0] => 18 [1] => 20 [2] => 25 ) The serial number automatically assigned by this system is called the key name. This array of key names is called the index. Array (indexed array).

Of course, you can also manually specify the key name:

$arr_age1 = array( 0 => 18, 1 => 20, 2 => 25 );

Note: Manually specifying key names does not need to start from 0, and you do not need to specify key names in numerical order. When a new unit is added to the array without specifying a key name, the system will automatically add 1 to the largest numeric key in the existing array as the key name of the new unit.

When strings rather than numeric indexes are used as keys, the array is called an associative array:

$arr_age2 = array("wang"=>18, "li"=>20, "zhang"=>25); But in PHP, there is no obvious boundary between these two arrays, and both can Mix it up. Note that associative arrays are case-sensitive for key names.

Output array cell value

The output array cell value can be accessed using the following method:

echo $arr_age1[0]; 
//Output: 18

echo $arr_age2["wang"];
//Output: 18 In some cases, for debugging, you may need to output the data and structure of the entire array. In this case, you need to use the print_r() or var_dump() function. For details, see PHP print_r and var_dump output array

Operation array unit

You can operate array units like ordinary variables, such as:

<&#63;php
$arr_age2 = array("wang"=>18, "li"=>20, "zhang"=>25);
$arr_age2["wang"] = $arr_age2["wang"] + 10;
&#63;>

Now $arr_age2 is:

Array ( [wang] => 28 [li] => 20 [zhang] => 25 )
To check if an array cell is set, use isset() .

Destroy array

Use the unset() function to destroy an array cell or an entire array:

<&#63;php
unset($arr_age1[0]);
unset($arr_age1);
&#63;> 

Multidimensional array

If the values ​​in the array are also arrays, we call such an array a recursive array or a multidimensional array.

Example:

<&#63;php
$all = array( "fruits" => array( "a"=>"orange", "b"=>"banana", "c"=>"apple"),
	"ages" => array( 18, 20, 25 )
	);
echo $all["fruits"]["c"];	//输出apple
echo $all["ages"][0];		//输出18
&#63;>

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