Counter Array in PHP

Question

I want to write a function that returns a counter array. That is, given an array of integers $A, in which the integers are in the range (0...$m) it should return an array of size $m + 1 in which each index has the number of occurrences of that index number in $A.

For instance, if:

$A = array(1, 4, 2, 2, 4, 2);
$m = 4;

It should output:

array(0, 1, 3, 0, 2)

I'm wondering if there is a built-in function to do this in PHP.

In python it would look something like:

def counting(A, m):
 n = len(A)
 count = [0] * (m + 1)
 for k in xrange(n):
 count[A[k]] += 1
 return count

• chris85: Maybe php.net/manual/en/function.array-count-values.php?
• u_mulder: No, write your own function. Also array_count_values can help
• Webomatik: Might have your answer here: stackoverflow.com/questions/1317612/…
• AbraCadaver: Any feedback for the answers?

Answer 1

You can try this:

$a = array(1, 4, 2, 2, 4, 2);
$m = 4;
function counting(Array $a, $m){
 // Create our result array
 $result = array();
 // Make sure m is an integer for version before PHP 7, otherwise return an empty array
 if(!is_int($m))
 return $result;
 // Get the count of each occurence in the array
 $counts = array_count_values($a);
 // Loop through each number of m
 for($i=0; $i<=$m; $i++)
 $result[$i] = isset($counts[$i]) ? $counts[$i] : 0;
 return $result;
}

The result of var_dump(counting($a, $m)):

array(5) {
 [0]=>
 int(0)
 [1]=>
 int(1)
 [2]=>
 int(3)
 [3]=>
 int(0)
 [4]=>
 int(2)
}

Answer 2

Try the below code

function count_array($array,$m){
 // count values
 $count_values = array_count_values($array);
 // loop for $m times
 for($i=0;$i<=$m;$i++){
 // check if there exits a key in the array
 if(array_key_exists($i,$count_values)){
 $result_array[$i] = $count_values[$i];
 }else{
 $result_array[$i] = 0;
 }
 }
 return $result_array;
}
$A = array(1, 4, 2, 2, 4, 2);
$m = 4;
$result = count_array($A,$m);

Out Put:

Array
(
[0] => 0
[1] => 1
[2] => 3
[3] => 0
[4] => 2
)

Answer 3

New version:

$result = array_replace(array_fill(0, $m+1, 0),
 array_slice(array_count_values($A), 0, $m-1, true));

• Replace an array of zeros with length $m+1 with a count of the values of $A up to length $m.

Original version:

$result = array_fill(0, $m+1, 0);
foreach($A as $i) {
 if(isset($result[$i])) {
 $result[$i]++;
 }
}

• Create a $result array of zeros with length $m+1
• Loop array $A and increment $result index of $A value

Obviously if you want a function just wrap code in:

function counting($A, $m) {
 //code
 return $result;
}