php gets the first few values ​​​​of an array

In PHP programming, it is often necessary to take the first few values ​​​​of an array. This can be done using PHP's built-in functions, the most commonly used of which is the array_slice() function. This function extracts a continuous range of values ​​from an array and returns a new array. Below we will introduce in detail how to use the array_slice() function to get the first few values ​​​​of the array.

1. The syntax of the array_slice() function

The syntax of the array_slice() function is as follows:

array array_slice ( array $array , int $offset [, int $length = NULL [, bool $preserve_keys = false ]] )

Parameter description:

$array: indicates the array to be extracted;

$offset: indicates extraction The starting position can be a positive integer or a negative integer. When it is a negative integer, it means extracting from the end;

$length: Indicates the length of the extraction, which can be a positive integer or a negative integer. When it is A negative integer means extracting from the starting position forward;

$preserve_keys: Indicates whether to retain the key names of the original array. The default is false, that is, not retained.

2. Get the first few values ​​​​of the array

Let’s first look at a simple example, as shown below:

$arr ​​= [1, 2, 3, 4, 5, 6, 7, 8, 9];
$length = 3;
$new_arr = array_slice($arr, 0, $length);
print_r($new_arr);
?>

Run the above code, the output result is:

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

In the above example, we define an array $arr containing 9 elements, and then use the array_slice() function to extract the first 3 values ​​​​of the array. We save the extracted value in the $new_arr variable and output the result. As you can see, a new array containing the first 3 elements is output. This is the basic operation of taking the first few values ​​​​of the array through the array_slice() function.

3. Get the last few values ​​of the array

In addition to getting the first few values ​​of the array, we can also get the last few values ​​of the array. This can be achieved by setting the $offset parameter to a negative number, as shown in the following example:

$arr ​​= [1, 2, 3, 4, 5, 6, 7, 8, 9];
$length = 3;
$new_arr = array_slice($arr, -$length, $length);
print_r($new_arr);
?>

Run the above code, the output result is:

Array ([0] => 7 [1] => 8 [2] => 9 )

In the above example, we Set the $offset parameter to a negative number to start extracting from the end of the array. We also set the $length parameter to 3, which means extracting 3 elements. This way you can get a new array containing the last 3 elements of the array.

4. Keep the key names of the original array

By default, the array_slice() function will re-index the extracted array, that is, the newly obtained array The key names will not be consistent with the original array. However, if we only need to extract elements without changing the key names, we can set the $preserve_keys parameter to true. The sample code is as follows:

$arr ​​= ['a' => ; 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5];
$length = 3;
$new_arr = array_slice($arr, 0, $length, true);
print_r($new_arr);
?>

Run the above code, the output result is:

Array ( [a] => 1 [b] => 2 [c] => 3 )

In the above example, we set the $preserve_keys parameter to true, which means that the key names of the original array are retained. In this way, you can get a new array containing the first three elements of the original array, and the key names remain unchanged.

5. Applicable Scenarios

In actual development, there are many scenarios where we need to take the first few values ​​​​of the array, such as:

(1 ) Display the latest articles or product lists;

(2) Display the most popular articles or product lists;

(3) Generate navigation bars or pagination links, etc.

In these scenarios, if we can quickly and easily retrieve the first few values ​​of the array, we can greatly simplify code writing and improve development efficiency.

6. Summary

By using the array_slice() function, we can easily take the first few values ​​​​or the last few values ​​​​of the array, and can retain the keys of the original array name. In actual development, we can make full use of this function to simplify code writing and improve development efficiency.

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