How to remove the first few lines of an array in php

Array is one of the most commonly used data structures in PHP. It can store a set of related data, and it is also very convenient to read and modify data. In actual development, sometimes it is necessary to remove the first few rows of the array. This operation is particularly useful when processing large data sets. This article will introduce how to use php to remove the first few lines of an array.

1. array_slice() function

In PHP, the array_slice() function is a very important function. It can select a section of elements from an array and return these elements. The syntax of the array_slice() function is as follows:

array array_slice ( array $array , int $offset [, int $length = NULL [, bool $preserve_keys = false ]] )

Among them, $array represents the original array, $offset represents the position from which to select elements, $length represents the number of selected elements, and $preserve_keys represents whether to retain the original array. key name. If $offset is negative, the offset is calculated from the end.

It is very simple to use the array_slice() function to remove the first few rows of the array. You only need to set $offset to the number of rows to be removed. For example, assume that the array $arr contains 10 elements, and we want to remove the first 3 elements. The code is as follows:

$arr = array(1,2,3,4,5,6,7,8,9,10);
$offset = 3;
$result = array_slice($arr, $offset);
print_r($result);

The output result is as follows:

Array (
  [0] => 4
  [1] => 5
  [2] => 6
  [3] => 7
  [4] => 8
  [5] => 9
  [6] => 10
)

As you can see, the $result array has been removed The first 3 elements are removed, leaving only the last 7 elements.

2. Loop through the array

In addition to using the array_slice() function, another way to remove the first few rows of the array is to loop through the array and delete the previous elements one by one. Although this method is more troublesome, it is also very practical in some specific situations.

Suppose we want to remove the first 2 elements of the array $arr. We can use a for loop to delete them one by one. The code is as follows:

$arr = array(1,2,3,4,5,6,7,8,9,10);
$del_count = 2;
for ($i = 0; $i < $del_count; $i++) {
    array_shift($arr);
}
print_r($arr);

The output result is as follows:

Array (
  [0] => 3
  [1] => 4
  [2] => 5
  [3] => 6
  [4] => 7
  [5] => 8
  [6] => 9
  [7] => 10
)

From the result, you can It can be seen that the first two elements of the array $arr have been deleted.

It should be noted that when looping through the array and deleting elements, pay attention to the index of the array changing. Therefore, it is recommended to first calculate the number of elements to be deleted and use the array_shift() function in a loop to delete elements. If you use the unset() function to delete elements, you need to manually rearrange the array index, which will be more troublesome.

3. Use the array_splice() function

The array_splice() function is similar to the array_slice() function. You can also select a segment of elements from the array and return these elements. The difference is that the array_splice() function can directly modify the original array instead of returning a new array.

The syntax of the array_splice() function is as follows:

array array_splice ( array &$input , int $offset [, int $length = NULL [, mixed $replacement = array() ]] )

Among them, $input represents the original array, $offset represents the starting position of the element to be selected, and $length represents the number of elements to be selected. , $replacement is an optional parameter, indicating the new element used to replace the selected element.

It is also very easy to use the array_splice() function to remove the first few rows of the array, just specify $offset. For example, to delete the first three elements of the array $arr, the code is as follows:

$arr = array(1,2,3,4,5,6,7,8,9,10);
$offset = 0;
array_splice($arr, $offset, 3);
print_r($arr);

The output result is as follows:

Array (
  [0] => 4
  [1] => 5
  [2] => 6
  [3] => 7
  [4] => 8
  [5] => 9
  [6] => 10
)

You can see that the first three elements of the array $arr have been deleted. .

It should be noted that the array_splice() function directly modifies the original array, so it should be used with caution to avoid unnecessary data loss. If you need to preserve the original array, it is recommended to make a copy first and then modify the copy.

Summary

This article introduces three methods to use PHP to remove the first few rows of an array, including using the array_slice() function, looping through the array and using the array_splice() function. These methods are very simple and easy to use, and developers can choose the appropriate method according to their own needs. It should be noted that when deleting array elements, pay attention to the change of index to avoid unnecessary errors.

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