How to query an array in php and get key-value pairs

In PHP, array is a very common data type that can save multiple elements and organize and access these elements in a certain way. Among them, key and value are two important components of the array. The key is used to uniquely identify each element in the array, and the value is the data associated with the key. In actual development, we often need to query a certain key-value pair in the array and obtain all key-value pairs in the array. This article will introduce in detail how to implement these operations.

1. Query a certain key-value pair in the array

1. Use isset() function to determine whether the key exists

In PHP, we can Use the isset() function to determine whether a key in the array exists. Returns true if the key exists, false otherwise. The sample code is as follows:

$fruits = array(
    "apple" => "red",
    "banana" => "yellow",
    "orange" => "orange"
);

if (isset($fruits["apple"])) {
    echo "apple exists\n";
} else {
    echo "apple does not exist\n";
}

The above code defines an associative array $fruits, which contains three elements, namely apples, bananas and oranges. Next, use the isset() function to determine whether there is an element with the key "apple" in the $fruits array. If it exists, output "apple exists", otherwise output "apple does not exist".

2. Use the array_key_exists() function to determine whether a key exists

In addition to using the isset() function, we can also use the array_key_exists() function to determine whether a key exists in the array Whether the key exists. The difference between the array_key_exists() function and the isset() function is that the former only determines whether the key exists, while the latter also determines whether the value corresponding to the key is null. The sample code is as follows:

$fruits = array(
    "apple" => "red",
    "banana" => "yellow",
    "orange" => "orange"
);

if (array_key_exists("apple", $fruits)) {
    echo "apple exists\n";
} else {
    echo "apple does not exist\n";
}

The above code is similar to the first method, except that the array_key_exists() function is used to determine whether there is an element with the key "apple" in the array.

3. Use the in_array() function to determine whether a value exists

Sometimes, we do not care about whether the key exists, but want to determine whether a certain value exists in the array. At this time, you can use the in_array() function to make a judgment. The sample code is as follows:

$fruits = array("apple", "banana", "orange");

if (in_array("apple", $fruits)) {
    echo "apple exists\n";
} else {
    echo "apple does not exist\n";
}

The above code defines a normal array $fruits, which contains three elements. Use the in_array() function to determine whether there is an element with the value "apple" in the array. If it exists, output "apple exists", otherwise output "apple does not exist".

2. Get all the key-value pairs in the array

1. Use foreach to loop through the array

Get all the key-value pairs in the array, the most common The best way is to use a foreach loop to traverse the array. The sample code is as follows:

$fruits = array(
    "apple" => "red",
    "banana" => "yellow",
    "orange" => "orange"
);

foreach ($fruits as $key => $value) {
    echo "$key is $value\n";
}

The above code defines an associative array $fruits, containing three elements. Use foreach to loop through the array and output each key-value pair.

2. Use the array_keys() and array_values() functions to obtain all keys and values ​​respectively

In addition to using the foreach loop, you can also use the array_keys() and array_values() functions Get all keys and values ​​in the array individually. The sample code is as follows:

$fruits = array(
    "apple" => "red",
    "banana" => "yellow",
    "orange" => "orange"
);

$keys = array_keys($fruits);
$values = array_values($fruits);

print_r($keys);
print_r($values);

The above code defines an associative array $fruits, containing three elements. Use the array_keys() and array_values() functions to get all the keys and values ​​in $fruits and save them into the $keys and $values ​​variables respectively. Finally, use the print_r() function to output the values ​​of these two variables.

3. Use the array_walk() function to traverse the array

In addition to using the foreach loop and array_keys(), array_values() functions, we can also use the array_walk() function to traverse array. The array_walk() function can perform a custom function on each key-value pair in the array. The sample code is as follows:

$fruits = array(
    "apple" => "red",
    "banana" => "yellow",
    "orange" => "orange"
);

function print_fruit($value, $key)
{
    echo "$key is $value\n";
}

array_walk($fruits, "print_fruit");

The above code defines an associative array $fruits, containing three elements. A function named print_fruit() is defined to output each key-value pair in the array. Use the array_walk() function, passing in the print_fruit() function as the second argument, to walk through the array and execute the custom function.

Summary

This article introduces how to query a certain key-value pair in an array in PHP and obtain all key-value pairs in the array. In actual development, we need to choose different methods according to specific business needs. If you only want to determine whether a certain key or value exists, you can use isset(), array_key_exists() and in_array() functions. If you want to get all key-value pairs, you can use a foreach loop, array_keys(), array_values() function, or array_walk() function. It should be noted that when using arrays, the appropriate array type (ordinary array or associative array) and appropriate array operation functions should be selected according to the specific situation to improve program performance and efficiency.

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