php remove duplicate values ​​from array

During the programming process, we often encounter the need to deduplicate arrays. In this case, PHP provides many functions for the purpose of deduplication, but different functions have different implementation methods, leading to some problems and hidden dangers. Below, we'll look at two of these methods to help you understand how to use them correctly in various situations.

Method 1: Use the array_unique() function

PHP provides the array_unique() function, which can remove duplication without changing the array key name. The parameter of this function is the array to be deduplicated and returns a new array that has been deduplicated. For example:

$arr = array('a'=>1,'b'=>2,'c'=>3,'d'=>2,'e'=>1);
$new_arr = array_unique($arr);
print_r($new_arr);

The output result is:

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

It is very simple to use the array_unique() function to remove duplicates. The function stores all elements of the array in a hash table, with the element value as the key, the first key in which the element value appears as the real key, and returns a new array. However, you may face the following two problems when using this function:

1. For floating point numbers, precision may be lost, resulting in incorrect comparison.
2. For complex arrays, the array_unique() function may not work properly.

Therefore, we need to use another method to deal with the above two situations.

Method 2: Use loop traversal

Loop through the array and store its elements in a new array. If there are duplicate elements, we will skip the element. For example:

$arr = array('a'=>1,'b'=>2,'c'=>3,'d'=>2,'e'=>1);
$new_arr = array();
foreach ($arr as $value) {
    if(!in_array($value,$new_arr)){
        $new_arr[] = $value;
    }
}
print_r($new_arr);

The output result is:

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

This method is suitable for various types of arrays without losing precision, and can handle complex arrays well. However, its disadvantage is that it is slow, especially when the number of array elements is large, the loop traversal efficiency will become very inefficient.

To sum up, no matter which method you use, you should choose the method that best suits your needs. If you need to simply deduplicate an array and don't need to worry about precision and complexity issues, then using the array_unique() function is the best choice. But if you need to process complex arrays or need to retain array key names, you should use the loop traversal method.

In addition, you can also consider using other optimization functions, such as array_diff_key() and array_intersect_key(), to better handle the array deduplication problem. No matter which method you choose, you should handle array deduplication with caution to prevent potential problems.

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