How to change the index of an array in php

In PHP, array is a very common and important data type. When we need to sort or filter certain elements in an array according to certain rules, we often encounter situations where we need to change the array index. This article will introduce how to change the index of an array using PHP.

1. What is an array index?

In PHP, the array index is usually a number or a string, which is used to access the elements in the array. By default, PHP assigns a numeric index to each element in the array, starting from 0 and increasing, for example:

$fruits = array("apple", "banana", "orange");
echo $fruits[0]; // 输出：apple
echo $fruits[1]; // 输出：banana
echo $fruits[2]; // 输出：orange

In the above code, $fruits Each element of the array Each element has a numeric index, which are 0, 1, and 2 respectively. These indexes are automatically generated, we can also specify the index manually, for example:

$fruits = array(0 => "apple", 1 => "banana", 2 => "orange");
echo $fruits[0]; // 输出：apple
echo $fruits[1]; // 输出：banana
echo $fruits[2]; // 输出：orange

In this case, we manually specify an index for each element.

2. Use array_values() to change the index

In some cases, we need to reorder the index of the array. For example, we may want to sort the elements in an array filtered according to a certain condition by element value, and put the sorted elements into a new array. In this case, we can use the array_values() function to rearrange the indexes of the array. Here is an example:

$fruits = array("banana", "apple", "orange");
sort($fruits);
$fruits_with_new_index = array_values($fruits);
print_r($fruits_with_new_index);

In the above code, we use the sort() function to sort the $fruits array and then use the array_values( ) function puts the sorted elements into the $fruits_with_new_index array and rearranges the index. Finally, we used the print_r() function to output the new array:

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

As you can see, the element index in the new array increases from 0, which is different from the index of the original array.

3. Use the array_combine() function to change the index

In some cases, we may need to use the value of one array as the index and the value of another array as the element to create a new array . At this time, you need to use the array_combine() function. The following is an example:

$keys = array("apple", "banana", "orange");
$values = array(1, 2, 3);
$fruits_with_new_index = array_combine($keys, $values);
print_r($fruits_with_new_index);

In the above code, we use the array_combine() function to The values ​​in the $keys array are used as indexes, the values ​​in the $values array are used as elements, and a new array $fruits_with_new_index is created.

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

You can see that the index in the new array is determined by the value in the $keys array, and the element is determined by the value in the $values array .

4. Use the unset() function to delete the element index

In some cases, we may need to delete the index of an element in the array so that the element does not occupy a position in the array. At this time, you need to use the unset() function. The following is an example:

$fruits = array("apple", "banana", "orange");
unset($fruits[1]);
print_r($fruits);

In the above code, we use the unset() function to delete $fruits The element at index 1 in the array. Finally, use the print_r() function to output the array after deleting the element:

Array
(
    [0] => apple
    [2] => orange
)

You can see that after deleting the element, the banana element with index 1 is deleted from the array, leaving The element indices of are 0 and 2 respectively.

Summary:
This article introduces how to use the array_values(), array_combine() and unset() functions in PHP to change The index of the array. Mastering these methods allows us to process data in arrays more flexibly and achieve more effects.

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