PHP array learning how to create arrays by filling

In the previous article "PHP Array Learning How to Create and Initialize a One-Dimensional Array (Detailed Code Explanation)", we introduced two conventional methods of creating an array: "Directly for the array Element assignment" and "array() function". Today we will talk about the creation of arrays and introduce two alternative methods of creating arrays. Let’s take a look.

In PHP, we can also create new arrays by filling. The main functions used are: array_fill() and array_fill_keys().

• array_fill(): will create a new array by filling the key value

• array_fill_keys(): will fill the key name and key Value method to create a new array

Let’s take a closer look at these two functions through code examples.

1. array_fill() function

<?php
$arr=array_fill(0,4,"hello");
var_dump($arr);
?>

array_fill($index, $number, $value)Function accepted 3 non-omitable parameters $index (starting index), $number (number of filling elements) and $value (key value used for filling) .

Among them, the $index parameter supports negative values, and the array index has the following three values:

• If it is a positive number, the array The index starts from the $index value and ends with the $index $number-1 value. For example, $index is 2, $number is 4, then the array index is: 2, 3, 4, 5.

• If 0, the array index starts from 0 and ends with the $number-1 value. For example, $index is 0, $number is 4, then the array index is: 0, 1, 2, 3.

• If it is negative, the array index is $index, 0, 1, 2, ..., $number-2 consists of. For example, $index is -2, $number is 4, then the array index is: -2, 0, 1, 2.

In the above example, the $index of array_fill(0,4,"hello") is 0 (the index starts from 0) , $number is 4 (the array has four elements), so the array index is: 0, 1, 2, 3; and $value is hello, Then the key values ​​of these four elements are hello, so the output result is:

Looking at two examples:

<?php
$arr=array_fill(3,4,"hello");
var_dump($arr);
?>

Analysis: The index starts from 3 and ends at 3 4-1=6. The key values ​​of the array are all hello, so the output result is:

<?php
$arr=array_fill(-2,4,"hello");
var_dump($arr);
?>

The output result is:

$valueThe parameter can not only be a single value/string , or it can be an array, then what is created is a two-dimensional array.

<?php
header("Content-type:text/html;charset=utf-8");
$arr=array_fill(0,4,array("张三",25,"男"));
var_dump($arr);
?>

The output result is:

2. array_fill_keys() function

<?php
$keys=array("a","b","c","d");
$arr=array_fill_keys($keys,"hello");
var_dump($arr);
?>

array_fill_keys($keys,$value)The function accepts 2 parameters that cannot be omitted $keys (an array containing the fill key name), $value( populate the key value).

Simply put, the array_fill_keys() function will use the elements in the $keys array as key names and $value as values ​​to fill a new array.

As can be seen from the above code example: the new array has four elements, and the key names are "a", "b", and "c##" #", "d"; the key values ​​of these four elements are all "hello", so the output result is:

# #array_fill_keys() is the same as the array_fill() function. The

value can also accept an array, so what is created is a two-dimensional array.

<?php
header("Content-type:text/html;charset=utf-8");
$keys=array("a","b","c","d");
$arr=array_fill_keys($keys,array("李四",21,"男"));
var_dump($arr);
?>