Detailed explanation of advanced operations of traversing arrays in PHP_PHP Tutorial

When traversing data in PHP, list, foreach, and each are generally used, but they may not be used in the following tutorials. Let me introduce to you some advanced examples of traversing arrays. I hope this method will be helpful to everyone. Helpful.

When learning programming language, always learn for, and then try to use while to write the effect of for and other exercises.

Let’s take a look at how to have the function of foreach before there is no foreach? Write (use while, list, and each to achieve).

See in this article: How to write the predecessor of PHP’s foreach

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代码如下	复制代码
//旧的写法 reset($attributes); while (list($key, $value) = each($attributes)) {     //do something } //PHP4版本新增 foreach ($attributes as $key => $value){    //do something }

//Old way of writing

reset($attributes);
while (list($key, $value) = each($attributes)) {

//do something

}

//New version of PHP4

代码如下	复制代码
Array (   [0] => Array     (       [name] => chess       [price] => 12.99     )   [1] => Array     (       [name] => checkers       [price] => 9.99     )   [2] => Array     (       [name] => backgammon       [price] => 29.99     ) )

foreach ($attributes as $key => $value){

//do something

}

代码如下	复制代码
function comparePrice($priceA, $priceB){     return $priceA['price'] - $priceB['price']; } usort($games, 'comparePrice');执行了该程序片段，数组就会被排序，结果如下所示： Array (   [0] => Array     (       [name] => checkers       [price] => 9.99     )   [1] => Array     (       [name] => chess       [price] => 12.99     )   [2] => Array     (       [name] => backgammon       [price] => 29.99     ) )

Multidimensional associative array sorting PHP provides some array sorting functions, such as sort(), ksort(), and asort(), but it does not provide sorting of multi-dimensional associative arrays. For example, an array like this:

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Array ( [0] => Array ( [name] => chess [price] => 12.99 ) [1] => Array ( [name] => checkers [price] => 9.99 ) [2] => Array ( [name] => backgammon [price] => 29.99 ) )

To sort the array in ascending order, you need to write a function yourself to compare prices, and then pass the function as a callback function to the usort() function to implement this function:

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function comparePrice($priceA, $priceB){ Return $priceA['price'] - $priceB['price']; } usort($games, 'comparePrice'); After executing this program fragment, the array will be sorted, and the result is as follows: Array ( [0] => Array ( [name] => checkers [price] => 9.99 ) [1] => Array ( [name] => chess [price] => 12.99 ) [2] => Array ( [name] => backgammon [price] => 29.99 ) )

To sort the array in descending order, just swap the positions of the two subtracted numbers in the comparePrice() function.

Traverse the array in reverse order
PHP's While Loop and For Loop are the most common methods of traversing an array. But how do you iterate over an array like the one below?

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代码如下	复制代码
Array (   [0] => Array     (       [name] => Board       [games] => Array         (           [0] => Array             (               [name] => chess               [price] => 12.99             )           [1] => Array             (               [name] => checkers               [price] => 9.99             )         )     ) )

Array

(

[0] => Array

代码如下	复制代码
$iterator = new RecursiveArrayIterator($games); iterator_apply($iterator, 'navigateArray', array($iterator)); function navigateArray($iterator) {  while ($iterator->valid()) {   if ($iterator->hasChildren()) {    navigateArray($iterator->getChildren());   } else {    printf("%s: %s", $iterator->key(), $iterator->current());   }   $iterator->next();  }  }

(

[name] => Board

[games] => Array

(
                              [0] => (
                                                                                                                                                                                                                                                                    [name] => chess
                                                                                                                                                                                                                                                                      [price] => )

          [1] => Array

(
                                                                                                                                                                                                                                                   [name] => checkers

                                                                                                                                                                                                                                                                                                  [price] => )

代码如下	复制代码
Array (   [0] => Array     (       [name] => checkers       [price] => 9.99     )   [1] => Array     (       [name] => chess       [price] => 12.99     )   [2] => Array     (       [name] => backgammon       [price] => 29.99     ) )

) ) )

There is an iterator class for collections in the PHP standard library. It can not only be used to traverse some heterogeneous data structures (such as file systems and database query result sets), but can also be used to iterate some embedded objects of unknown size. Traversal of arrays. For example, to traverse the above array, you can use the RecursiveArrayIterator iterator:

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$iterator = new RecursiveArrayIterator($games); iterator_apply($iterator, 'navigateArray', array($iterator)); function navigateArray($iterator) { while ($iterator->valid()) { if ($iterator->hasChildren()) { NavigateArray($iterator->getChildren()); } else { Printf("%s: %s", $iterator->key(), $iterator->current()); } $iterator->next(); } }

Executing this code will give the following results: name: Board name: chess price: 12.99 name: checkers price: 9.99 Filter the results of associative arrays Suppose you are given the following array, but you only want to operate on elements whose price is less than $11.99:

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Array ( [0] => Array ( [name] => checkers [price] => 9.99 ) [1] => Array ( [name] => chess [price] => 12.99 ) [2] => Array ( [name] => backgammon [price] => 29.99 ) )

It can be easily implemented using the array_reduce() function:

The code is as follows

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代码如下	复制代码
function filterGames($game){  return ($game['price'] } $names = array_filter($games, 'filterGames');

function filterGames($game){

return ($game['price'] }

代码如下	复制代码
Array (   [1] => Array     (       [name] => checkers       [price] => 9.99     ) )

$names = array_filter($games, 'filterGames');

The array_reduce() function will filter out all elements that do not satisfy the callback function. The callback function in this example is filterGames. Any element with a price lower than 11.99 will be kept, and the others will be eliminated. The execution result of this code segment:

代码如下	复制代码
class Game {  public $name;  public $price; } $game = new Game(); $game->name = 'chess'; $game->price = 12.99; print_r(array($game));执行该例子就会产生如下结果： Array ( [0] => Game Object   (     [name] => chess     [price] => 12.99   ) )

Convert object to array

代码如下	复制代码
class Game {  public $name;  private $_price;  public function setPrice($price)  {   $this->_price = $price;  } } $game = new Game(); $game->name = 'chess'; $game->setPrice(12.99); print_r(array($game));执行该代码片段： Array ( [0] => Game Object   (     [name] => chess     [_price:Game:private] => 12.99   ) )

One requirement is to convert the object into an array form. The method is much simpler than you think, just force conversion is enough! Example:

The code is as follows

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class Game {

public $name;
public $price;

}

代码如下	复制代码
$arr = array(  0=>'madden2011.png',  1=>'madden2011-1.png',  2=>'madden2011-2.png',  3=>'madden2012.png' );

$game = new Game(); $game->name = 'chess'; $game->price = 12.99; print_r(array($game)); executing this example will produce the following results: Array ( [0] => Game Object ( [name] => chess [price] => 12.99 ) )

Converting objects to arrays can have some unpredictable side effects. For example, in the above code snippet, all member variables are of public type, but the return results for private variables will be different. Here is another example:

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class Game { public $name; private $_price; public function setPrice($price) { $this->_price = $price; } } $game = new Game(); $game->name = 'chess'; $game->setPrice(12.99); print_r(array($game));Execute this code snippet: Array ( [0] => Game Object ( [name] => chess [_price:Game:private] => 12.99 ) )

As you can see, in order to distinguish, the keys of the private variables saved in the array are automatically changed. "Natural ordering" of arrays PHP's sorting results for "alphanumeric" strings are undefined. For example, suppose you have many image names stored in an array:

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$arr = array( 0=>'madden2011.png', 1=>'madden2011-1.png', 2=>'madden2011-2.png', 3=>'madden2012.png' );

How do you sort this array? If you use sort() to sort the array, the result is like this:

代码如下	复制代码
Array (     [0] => madden2011-1.png     [1] => madden2011-2.png     [2] => madden2011.png     [3] => madden2012.png )

Sometimes this is what we want, but what if we want to keep the original subscript? To solve this problem, you can use the natsort() function, which sorts the array in a natural way:

The code is as follows

代码如下	复制代码
$arr = array(  0=>'madden2011.png',  1=>'madden2011-1.png',  2=>'madden2011-2.png',  3=>'madden2012.png' ); natsort($arr); echo " "; print_r($arr); echo " "; ?> 运行结果： Array (     [1] => madden2011-1.png     [2] => madden2011-2.png     [0] => madden2011.png     [3] => madden2012.png )

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$arr = array(
0=>'madden2011.png',
1=>'madden2011-1.png',
2=>'madden2011-2.png',
3=>'madden2012.png'
);

natsort($arr);
echo "

"; print_r($arr); echo "

";
?>

Run result: Array
(
[1] => madden2011-1.png
[2] => madden2011-2.png
[0] => madden2011.png
[3] => madden2012.png
)

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truehttp: //www.bkjia.com/PHPjc/632897.htmlTechArticleTraversing data in php generally uses one of list, foreach, and each, but the following tutorial may I won’t use it. Let me introduce to you some advanced examples of traversing arrays. I hope...