(PHP 4, PHP 5, PHP 7)
count — 计算数组中的单元数目，或对象中的属性个数
统计出数组里的所有元素的数量，或者对象里的东西。
对于对象，如果安装了 SPL，可以通过实现 Countable 接口对 count()挂钩（hook） 。该接口只有一个方法 Countable::count()，此方法为 count() 函数返回值。
关于 PHP 中如何实现和使用数组可以参考手册中数组章节中的详细描述。
array_or_countable数组或者 Countable 对象。
mode
如果可选的 mode 参数设为
COUNT_RECURSIVE（或 1），count()
将递归地对数组计数。对计算多维数组的所有单元尤其有用。
count() 能检测递归来避免无限循环，但每次出现时会产生 E_WARNING 错误
（如果 array 不止一次包含了自身）并返回大于预期的统计数字。
返回 array_or_countable 中的单元数目。
如果参数既不是数组，也不是实现
Countable 接口的对象，将返回
1。
有个例外：如果
array_or_countable 是 NULL 则结果是 0。
count() 对没有初始化的变量返回 0，但对于空的数组也会返回 0。 用 isset() 来测试变量是否已经初始化。
Example #1 count() 例子
<?php
$a[0] = 1;
$a[1] = 3;
$a[2] = 5;
$result = count($a);
// $result == 3
$b[0] = 7;
$b[5] = 9;
$b[10] = 11;
$result = count($b);
// $result == 3
$result = count(null);
// $result == 0
$result = count(false);
// $result == 1
?>
Example #2 递归 count() 例子
<?php
$food = array('fruits' => array('orange', 'banana', 'apple'),
'veggie' => array('carrot', 'collard', 'pea'));
// recursive count
echo count($food, COUNT_RECURSIVE); // output 8
// normal count
echo count($food); // output 2
?>
To count items in multidem. array with specific key you can use:
$groups = [
[
'id' => 1,
'name' => 'group 1',
'items' => ['a','b','c','d'],
],
[
'id' => 2,
'name' => 'group 2',
'items' => ['e','f','g'],
]
];
$items_total = array_sum(array_map(function($v){return count($v['items']);},$groups)); // Result is 7.
Don't use count($array) if you want to check whether it's empty. Use empty($array) instead:
Stats for 100000000 iterations:
Empty($arr): 7.0643041133881s
Count($arr) === 0: 11.981563091278s
!count($arr): 11.872883081436s
$arr === []: 9.6288840770721s
with an empty whereas $arr is empty.
Test script:
<?php
$test = [];
$startTime = microtime(true);
for($i = 0; $i <= 100000000; $i++) {
if(empty($test)) {
}
}
$time = microtime(true) - $startTime;
echo 'empty($arr): ' . $time . 's' . PHP_EOL;
$startTime = microtime(true);
for($i = 0; $i <= 100000000; $i++) {
if(count($test) === 0) {
}
}
$time = microtime(true) - $startTime;
echo 'count($arr) === 0: ' . $time . 's' . PHP_EOL;
$startTime = microtime(true);
for($i = 0; $i <= 100000000; $i++) {
if(!count($test)) {
}
}
$time = microtime(true) - $startTime;
echo '!count($arr): ' . $time . 's'. PHP_EOL;
$startTime = microtime(true);
for($i = 0; $i <= 100000000; $i++) {
if($test === []) {
}
}
$time = microtime(true) - $startTime;
echo '$arr === []: ' . $time . 's'. PHP_EOL;
count(false); // Returns 1, not 0.
You can not get collect sub array count when use the key on only one sub array in an array:
$a = array("a"=>"appple", b"=>array('a'=>array(1,2,3),'b'=>array(1,2,3)));
$b = array("a"=>"appple", "b"=>array(array('a'=>array(1,2,3),'b'=>array(1,2,3)), array(1,2,3),'b'=>array(1,2,3)), array('a'=>array(1,2,3),'b'=>array(1,2,3))));
echo count($a['b']); // 2 NOT 1, expect 1
echo count($b['b']); // 3, expected
You can not get collect sub array count when there is only one sub array in an array:
$a = array ( array ('a','b','c','d'));
$b = array ( array ('a','b','c','d'), array ('e','f','g','h'));
echo count($a); // 4 NOT 1, expect 1
echo count($b); // 2, expected
All the previous recursive count solutions with $depth option would not avoid infinite loops in case the array contains itself more than once.
Here's a working solution:
<?php
/**
* Recursively count elements in an array. Behaves exactly the same as native
* count() function with the $depth option. Meaning it will also add +1 to the
* total count, for the parent element, and not only counting its children.
* @param $arr
* @param int $depth
* @param int $i (internal)
* @return int
*/
public static function countRecursive(&$arr, $depth = 0, $i = 0) {
$i++;
/**
* In case the depth is 0, use the native count function
*/
if (empty($depth)) {
return count($arr, COUNT_RECURSIVE);
}
$count = 0;
/**
* This can occur only the first time when the method is called and $arr is not an array
*/
if (!is_array($arr)) {
return count($arr);
}
// if this key is present, it means you already walked this array
if (isset($arr['__been_here'])) {
return 0;
}
$arr['__been_here'] = true;
foreach ($arr as $key => &$value) {
if ($key !== '__been_here') {
if (is_array($value) && $depth > $i) {
$count += self::countRecursive($value, $depth, $i);
}
$count++;
}
}
// you need to unset it when done because you're working with a reference...
unset($arr['__been_here']);
return $count;
}
?>
/** Count of objects */
class ABC{ }
$objecto = new ABC();
$total = count((array)$object); //Returns Zero.
$total = count($object); //Returns One
echo $total;
About 2d arrays, you have many way to count elements :
<?php
$MyArray = array ( array(1,2,3),
1,
'a',
array('a','b','c','d') );
// All elements
echo count($MyArray ,COUNT_RECURSIVE); // output 11 (9 values + 2 arrays)
// First level elements
echo count($MyArray ); // output 4 (2 values+ 2 arrays)
// Both level values, but only values
echo(array_sum(array_map('count',$MyArray ))); //output 9 (9 values)
// Only second level values
echo (count($MyArray ,COUNT_RECURSIVE)-count($MyArray )); //output 7 ((all elements) - (first elements))
?>
A function of one line to find the number of elements that are not arrays, recursively :
function count_elt($array, &$count=0){
foreach($array as $v) if(is_array($v)) count_elt($v,$count); else ++$count;
return $count;
}
As I see in many codes, don't use count to iterate through array.
Onlyranga says you could declare a variable to store it before the for loop.
I agree with his/her approach, using count in the test should be used ONLY if you have to count the size of the array for each loop.
You can do it in the for loop too, so you don't have to "search" where the variable is set.
e.g.
<?php
$array = [1, 5, 'element'];
for($i = 0, $c = count($array); $i < $c; $i++)
var_dump($array[$i]);
?>
[Editor's note: array at from dot pl had pointed out that count() is a cheap operation; however, there's still the function call overhead.]
If you want to run through large arrays don't use count() function in the loops , its a over head in performance, copy the count() value into a variable and use that value in loops for a better performance.
Eg:
// Bad approach
for($i=0;$i<count($some_arr);$i++)
{
// calculations
}
// Good approach
$arr_length = count($some_arr);
for($i=0;$i<$arr_length;$i++)
{
// calculations
}
Get maxWidth and maxHeight of a two dimensional array..?
Note:
1st dimension = Y (height)
2nd dimension = X (width)
e.g. rows and cols in database result arrays
<?php
$TwoDimensionalArray = array( 0 => array( 'key' => 'value', ...), ... );
?>
So for Y (maxHeight)
<?php
$maxHeight = count( $TwoDimensionalArray )
?>
And for X (maxWidth)
<?php
$maxWidth = max( array_map( 'count', $TwoDimensionalArray ) );
?>
Simple? ;-)
I actually find the following function more useful when it comes to multidimension arrays when you do not want all levels of the array tree.
// $limit is set to the number of recursions
<?php
function count_recursive ($array, $limit) {
$count = 0;
foreach ($array as $id => $_array) {
if (is_array ($_array) && $limit > 0) {
$count += count_recursive ($_array, $limit - 1);
} else {
$count += 1;
}
}
return $count;
}
?>
My function returns the number of elements in array for multidimensional arrays subject to depth of array. (Almost COUNT_RECURSIVE, but you can point on which depth you want to plunge).
<?php
function getArrCount ($arr, $depth=1) {
if (!is_array($arr) || !$depth) return 0;
$res=count($arr);
foreach ($arr as $in_ar)
$res+=getArrCount($in_ar, $depth-1);
return $res;
}
?>