How to traverse the same array in php

In PHP, traversing an array is a very common operation. We usually want to use this method to find elements in an array, operate on an array, or output all elements in an array. In some cases, we need to find those elements with the same value to perform some other operations. This article will explore in detail how to traverse the same array in PHP.

First look at the two methods of traversing arrays in PHP:

1. foreach loop

The foreach loop is the most common method of traversing arrays in PHP , its basic syntax structure is as follows:

foreach (array_expression as $key => $value) {
  // code to be executed;
}

• array_expression: the array to be traversed
• $key: the key of the current element
• $value: The value of the current element

The foreach loop will traverse each element in the array in turn and assign its key and value to $key and $value, and then execute the corresponding code.

As a simple example, we have an array:

$arr = array(2, 4, 6, 8, 10);

Use a foreach loop to traverse this array and output each element:

foreach ($arr as $value) {
  echo $value . "<br>";
}

The output is as follows:

2
4
6
8
10

2. for loop

The for loop is also a common way to traverse an array in PHP, similar to the usual for loop. The basic syntax structure is as follows:

for ($i = 0; $i < count($array); $i++) {
  // code to be executed;
}

• $array: the array to be traversed
• $i: the index of the current element

The for loop will use the count() function to count the number of elements in the array and store it in the variable $i, and then iterate through each element in the array. elements.

As a simple example, we have the same array as above:

$arr = array(2, 4, 6, 8, 10);

Use a for loop to traverse this array and output each element:

for ($i = 0; $i < count($arr); $i++) {
  echo $arr[$i] . "<br>";
}

The output is as follows:

2
4
6
8
10

The above are the basic methods of traversing arrays in PHP. Below we will introduce how to traverse the same array.

1. Use the array_count_values() function

The array_count_values() function can find elements with the same value in an array. Its basic syntax structure is as follows:

array array_count_values ( array $array )

• $array: the array to be found

This function will return a new array containing The number of occurrences of each element in the original array. To give a simple example, we have an array:

$arr = array(1, 2, 3, 4, 3, 2, 1, 5);

Use the array_count_values() function to find the same elements:

$newArr = array_count_values($arr);
print_r($newArr);

The output is as follows:

Array
(
    [1] => 2
    [2] => 2
    [3] => 2
    [4] => 1
    [5] => 1
)

You can see from the output Out, the new array contains the number of occurrences of each element in the original array, of which elements 1, 2, and 3 appear twice, and elements 4 and 5 only appear once.

2. Using a foreach loop

Another way to iterate through the same elements in an array is to use a foreach loop. The specific idea is to use a nested foreach loop. Each time it traverses an array element, it traverses the elements behind it and compares whether their values ​​are the same. To give a simple example, we have an array:

$arr = array(1, 2, 3, 4, 3, 2, 1, 5);

Use a foreach loop to traverse this array and find the same elements:

$sameArr = array();
foreach ($arr as $key1 => $value1) {
  foreach ($arr as $key2 => $value2) {
    if ($key1 < $key2 && $value1 == $value2) {
      $sameArr[] = $value1;
    }
  }
}
print_r($sameArr);

The output is as follows:

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

From As can be seen from the output, the same elements 2, 3, and 1 in the original array were found. In fact, this method is more troublesome and more time-consuming when processing large arrays. It is recommended to use the array_count_values() function.

The above are two methods of traversing the same array in PHP. I hope it will be helpful to you.

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