Why can't array values ​​be repeated in php? How to avoid it?

PHP array is a commonly used data type used to store large amounts of data and perform operations. There are some basic rules to follow when working with PHP arrays. One of them is that array values ​​cannot be repeated. This means that you cannot use the same value as a key or element in the same array.

Why array values ​​cannot be repeated?

An array is a special variable type that can store many different types of values. In PHP, arrays can be used to store numbers, strings, objects, etc. In an array, each element has a unique key and value. Keys can be repeated, but values ​​cannot be repeated, otherwise conflicts will occur.

For example, if you have an array that stores a list of students, each student name is the value of an element. If two students have the same name, their position in the array will not be determined, which will lead to confusion and errors. Therefore, in order to avoid this situation, the values ​​of the array must be unique.

How to avoid duplication of array values?

PHP provides some methods to ensure the uniqueness of array values. Here are some of the available methods:

1. Using the array_unique() function

This function can be used to remove duplicate values ​​from an array. It returns a new array in which each value appears only once. For example, the following code demonstrates how to use the array_unique() function:

$names = array("John", "Mary", "David", "Mary", "John");
$names = array_unique($names);
print_r($names);

Output results:

Array
(
    [0] => John
    [1] => Mary
    [2] => David
)

2. Using the in_array() function

This function Can be used to check if a value already exists in the array. If the values ​​are duplicated, appropriate action can be taken. For example, the following code demonstrates how to use the in_array() function:

$names = array("John", "Mary", "David");

if(in_array("Mary", $names)) {
    echo "Mary is already in the array";
} else {
    array_push($names, "Mary");
}

print_r($names);

Output results:

Mary is already in the array
Array
(
    [0] => John
    [1] => Mary
    [2] => David
)

3. Using the array_search() function

This function Can be used to find a value in an array and return the key of that value. If the values ​​are duplicated, appropriate action can be taken. For example, the following code demonstrates how to use the array_search() function:

$names = array("John", "Mary", "David");

$key = array_search("Mary", $names);

if($key !== false) {
    echo "Mary is already in the array at index $key";
} else {
    array_push($names, "Mary");
}

print_r($names);

Output results:

Mary is already in the array at index 1
Array
(
    [0] => John
    [1] => Mary
    [2] => David
)

Summary

When using PHP arrays, It is very important to avoid duplicate values. You can use functions such as array_unique(), in_array(), and array_search() to ensure the uniqueness of array values. When writing code, please pay attention to whether the values ​​of the array are unique, this will help avoid unnecessary errors.

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