Loop through array keys php

Question

Warning: the benchmark below is not accurate that makes its results wrong.

Nội dung chính Show

Unpacking nested arrays with list()
How do I loop through an array of objects in PHP?
How can we store values from for loop into an array in PHP?
What is foreach loop in PHP?
How do you loop through a multidimensional array in PHP?

From my quick and dirty benchmark I did the following 50 times:

Solution 1 (worst):

foreach (array_keys($array) as $array_key) {
  echo $array_key;
}

Size of array: 1000000

Min: 0.11363291740417
Avg: 0.11681462287903
Max: 0.14569497108459

Size of array: 9999999

Min: 1.3098199367523
Avg: 1.3250577354431
Max: 1.3673560619354

Solution 2 (middle):

foreach ($array as $array_key => $array_value) {
  echo $array_key;
}

Size of array: 1000000

Min: 0.10167503356934
Avg: 0.10356130123138
Max: 0.11027193069458

Size of array: 9999999

Min: 1.2077870368958
Avg: 1.2256314325333
Max: 1.2829539775848

Solution 3 (best):

$array_keys = array_keys($array);
foreach ($array_keys as $array_key) {
  echo $array_key;
}

Size of array: 1000000

Min: 0.090911865234375
Avg: 0.092938437461853
Max: 0.097810983657837

Size of array: 9999999

Min: 1.0793349742889
Avg: 1.0941110134125
Max: 1.1402878761292

So you can see solution 3 is the quickest option if you only want to look through array keys :)

Hope this helps.

Code:

size_of_array = $size_of_array;
    echo 'Size of array: ' .  $this->size_of_array . PHP_EOL;
  }
  
  private function solution1() {
    $array = range(0, $this->size_of_array - 1);
    ob_start();
    $start = microtime(true);
    foreach (array_keys($array) as $array_key) {
      echo $array_key;
    }
    $finish = microtime(true) - $start;
    $echod = ob_get_clean();
    $this->results['solution1'][] = $finish;
  }

  private function solution2() {
    $array = range(0, $this->size_of_array - 1);
    ob_start();
    $start = microtime(true);
    foreach ($array as $array_key => $array_value) {
      echo $array_key;
    }
    $finish = microtime(true) - $start;
    $echod = ob_get_clean();
    $this->results['solution2'][] = $finish;
  }

  private function solution3() {
    $array = range(0, $this->size_of_array - 1);
    $array_keys = array_keys($array);
    ob_start();
    $start = microtime(true);
    foreach ($array_keys as $array_key) {
      echo $array_key;
    }
    $finish = microtime(true) - $start;
    $echod = ob_get_clean();
    $this->results['solution3'][] = $finish;
  }

  public function benchmark() {
    $this->solution1();
    $this->solution2();
    $this->solution3();
  }

  public function getResults()
  {
    echo PHP_EOL . 'Solution 1:' . PHP_EOL;
    echo 'Min: ' . min($this->results['solution1']) . PHP_EOL;
    echo 'Avg: ' . array_sum($this->results['solution1']) / count($this->results['solution1']) . PHP_EOL;
    echo 'Max: ' . max($this->results['solution1']) . PHP_EOL;

    echo PHP_EOL . 'Solution 2:' . PHP_EOL;
    echo 'Min: ' . min($this->results['solution2']) . PHP_EOL;
    echo 'Avg: ' . array_sum($this->results['solution2']) / count($this->results['solution2']) . PHP_EOL;
    echo 'Max: ' . max($this->results['solution2']) . PHP_EOL;

    echo PHP_EOL . 'Solution 3:' . PHP_EOL;
    echo 'Min: ' . min($this->results['solution3']) . PHP_EOL;
    echo 'Avg: ' . array_sum($this->results['solution3']) / count($this->results['solution3']) . PHP_EOL;
    echo 'Max: ' . max($this->results['solution3']) . PHP_EOL;
  }
}

$benchmarker = new DirtyBenchmarker(1000000);
$runs = 50;
for ($i = 0; $i < $runs; $i++) {
  $benchmarker->benchmark();
}
$benchmarker->getResults();

$benchmarker = new DirtyBenchmarker(9999999);
$runs = 50;
for ($i = 0; $i < $runs; $i++) {
  $benchmarker->benchmark();
}
$benchmarker->getResults();

(PHP 4, PHP 5, PHP 7, PHP 8)

The foreach construct provides an easy way to iterate over arrays. foreach works only on arrays and objects, and will issue an error when you try to use it on a variable with a different data type or an uninitialized variable. There are two syntaxes:

foreach (iterable_expression as $value)
    statement
foreach (iterable_expression as $key => $value)
    statement

The first form traverses the iterable given by iterable_expression. On each iteration, the value of the current element is assigned to $value.

The second form will additionally assign the current element's key to the $key variable on each iteration.

Note that foreach does not modify the internal array pointer, which is used by functions such as current() and key().

It is possible to customize object iteration.

In order to be able to directly modify array elements within the loop precede $value with &. In that case the value will be assigned by reference.

$arr = array(1, 2, 3, 4); foreach ($arr as &$value) { $value = $value * 2; } // $arr is now array(2, 4, 6, 8) unset($value); // break the reference with the last element ?>

Warning

Reference of a $value and the last array element remain even after the foreach loop. It is recommended to destroy it by unset(). Otherwise you will experience the following behavior:

$arr = array(1, 2, 3, 4); foreach ($arr as &$value) { $value = $value * 2; } // $arr is now array(2, 4, 6, 8)

// without an unset($value), $value is still a reference to the last item: $arr[3]

foreach ($arr as $key => $value) {
    // $arr[3] will be updated with each value from $arr...
    echo "{$key} => {$value} ";
    print_r($arr);
}
// ...until ultimately the second-to-last value is copied onto the last value// output:
// 0 => 2 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 2 )
// 1 => 4 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 4 )
// 2 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 )
// 3 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 )?>

It is possible to iterate a constant array's value by reference:

foreach (array(1, 2, 3, 4) as &$value) { $value = $value * 2; } ?>

Note:
foreach does not support the ability to suppress error messages using @.

Some more examples to demonstrate usage:

/* foreach example 1: value only */$a = array(1, 2, 3, 17);

foreach (

$a as $v) {
    echo "Current value of \$a: $v.\n";
}/* foreach example 2: value (with its manual access notation printed for illustration) */$a = array(1, 2, 3, 17);$i = 0; /* for illustrative purposes only */foreach ($a as $v) {
    echo "\$a[$i] => $v.\n";
    $i++;
}/* foreach example 3: key and value */$a = array(
    "one" => 1,
    "two" => 2,
    "three" => 3,
    "seventeen" => 17
);foreach ($a as $k => $v) {
    echo "\$a[$k] => $v.\n";
}/* foreach example 4: multi-dimensional arrays */
$a = array();
$a[0][0] = "a";
$a[0][1] = "b";
$a[1][0] = "y";
$a[1][1] = "z";foreach ($a as $v1) {
    foreach ($v1 as $v2) {
        echo "$v2\n";
    }
}/* foreach example 5: dynamic arrays */foreach (array(1, 2, 3, 4, 5) as $v) {
    echo "$v\n";
}
?>

Unpacking nested arrays with list()

(PHP 5 >= 5.5.0, PHP 7, PHP 8)

It is possible to iterate over an array of arrays and unpack the nested array into loop variables by providing a list() as the value.

For example:

$array = [ [1, 2], [3, 4], ];

foreach (

$array as list($a, $b)) {
    // $a contains the first element of the nested array,
    // and $b contains the second element.
    echo "A: $a; B: $b\n";
}
?>

The above example will output:

You can provide fewer elements in the list() than there are in the nested array, in which case the leftover array values will be ignored:

$array = [ [1, 2], [3, 4], ];

foreach (

$array as list($a)) {
    // Note that there is no $b here.
    echo "$a\n";
}
?>

The above example will output:

A notice will be generated if there aren't enough array elements to fill the list():

$array = [ [1, 2], [3, 4], ];

foreach (

$array as list($a, $b, $c)) {
    echo "A: $a; B: $b; C: $c\n";
}
?>

The above example will output:

Notice: Undefined offset: 2 in example.php on line 7
A: 1; B: 2; C: 

Notice: Undefined offset: 2 in example.php on line 7
A: 3; B: 4; C:

Sanusi Hassan ¶

8 days ago

destructure array elements

you can unpac nested array elements using the following

$array = [ [1, 2], [3, 4], ];

foreach (

$array as $v) {
    [$a, $b] = $v;
    echo "A: $a; B: $b\n";
}
?>

Okafor Chiagozie ¶

5 days ago

An easier way to unpack nested array elements

$array = [ [1, 2], [3, 4], ];

foreach ($array as [$a, $b]) { echo "A: $a; B: $b\n"; }

How do I loop through an array of objects in PHP?

6 ways to loop through an array in php.

while(expression){ // Code to be executed }.

do { // Code to be executed } while(expression);.

for (expr1; expr2; expr3) { //Code to be executed }.

array_walk(array|object &$array, callable $callback, mixed $arg = null): bool..

How can we store values from for loop into an array in PHP?

Declare the $items array outside the loop and use $items[] to add items to the array: $items = array(); foreach($group_membership as $username) { $items[] = $username; } print_r($items); Hope it helps!!

What is foreach loop in PHP?

PHP foreach loop is utilized for looping through the values of an array. It loops over the array, and each value for the fresh array element is assigned to value, and the array pointer is progressed by one to go the following element in the array.

How do you loop through a multidimensional array in PHP?

Looping through multidimensional arrays Just as with regular, single-dimensional arrays, you can use foreach to loop through multidimensional arrays. To do this, you need to create nested foreach loops — that is, one loop inside another: The outer loop reads each element in the top-level array.

programming php Foreach PHP

Loop through array keys php

Unpacking nested arrays with list()

How do I loop through an array of objects in PHP?

How can we store values from for loop into an array in PHP?

What is foreach loop in PHP?

How do you loop through a multidimensional array in PHP?

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