How to add key-value pairs in php array

In PHP, array is a very powerful and commonly used data structure. Sometimes, we may need to add key-value pairs to an array to make the array more complete and useful. This article will introduce how to add key-value pairs to a PHP array.

Basic concepts of PHP arrays

In PHP, an array is an ordered, key-value pair mapping structure. Each element in the array has a unique key (index), which can be a number or a string type.

Arrays are usually used to store a series of related data. For example, suppose we want to store the names and population of some cities. We can use an array to represent it:

$cities = [
    "New York" => 8399000,
    "Los Angeles" => 3999000,
    "Chicago" => 2705000,
    "Houston" => 2325000,
    "Phoenix" => 1660000
];

In this array, the name of the city is used as the key and the population is used as the value. We can access the corresponding value through the key, for example:

echo $cities["New York"]; // 输出 8399000

Add key-value pairs to PHP array

We can use a series of statements to add key-value pairs in the PHP array. The following are commonly used methods.

1. Direct assignment

First, we can use the equal sign to directly add key-value pairs to an array. For example:

// 初始化一个空数组
$fruits = [];

// 添加元素
$fruits["apple"] = 1;
$fruits["banana"] = 2;
$fruits["orange"] = 3;

// 输出
print_r($fruits);

In this example, we add $fruits["apple"] = 1, $fruits["banana"] = 2 and $fruits["orange"] = 3 to the $fruits array. Three key-value pairs were added. The final output is:

Array
(
    [apple] => 1
    [banana] => 2
    [orange] => 3
)

2. array_push() function

We can also use the array_push() function to add elements to an existing array. This function adds one or more elements to the end of the array and returns the length of the new array.

The following is an example:

$numbers = [1, 2, 3];

// 使用 array_push() 函数添加元素
array_push($numbers, 4, 5);

// 输出
print_r($numbers);

The output result is:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
)

3. Add key-value pairs in the loop

Sometimes , we may need to add elements to the array in a loop. In this case, we need to add the element to the end of the array using array[] = value statement.

The following is an example:

$colors = ["red", "green", "blue"];
$animals = ["cat", "dog", "fish"];

// 将 $colors 数组中的元素添加到 $animals 数组中
foreach ($colors as $color) {
    $animals[] = $color;
}

// 输出
print_r($animals);

The output result is:

Array
(
    [0] => cat
    [1] => dog
    [2] => fish
    [3] => red
    [4] => green
    [5] => blue
)

4. Use the array_merge() function

Finally, we can Use the array_merge() function to merge two or more arrays into one. The merged array contains all array elements, with only the last duplicate element retained.

The following is an example:

$fruits = ["apple" => 1, "orange" => 2];
$vegetables = ["carrot" => 3, "tomato" => 4];

// 合并两个数组
$foods = array_merge($fruits, $vegetables);

// 输出
print_r($foods);

The output result is:

Array
(
    [apple] => 1
    [orange] => 2
    [carrot] => 3
    [tomato] => 4
)

In the above method, the array_merge() function merges the $fruits and $vegetables arrays into a new array $foods. The elements of the new array contain the elements of both arrays.

Summary

In PHP, we can add elements to an array using methods such as the equal sign, the array_push() function, adding statements at the end of the array, and the array_merge() function. These methods are simple and easy to understand, and are often used in actual programming. Through these methods, we can make PHP arrays more complete and useful, providing better data structure support for our programs.

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