Find the most frequent number in PHP array - php

Question

I have an array in PHP with repeating numbers and I would like to find the most frequent but only when there is only one of that.
while (count(array_count_values($arr)) > 1) {
$minim = min(array_count_values($arr));
while ($minim == min(array_count_values($arr))) {
unset($arr[array_search(array_search(min(array_count_values($arr)), array_count_values($idList)), $arr)]);
$arr = array_splice($arr, 0, 1);
}
}
In my code the first while runs until I have only one number (multiple times) in the array and with the second one I delete the less frequent numbers.
My problem is the I get this error for my second min(): "Array must contain at least one element".

Answer 1

I have an array in PHP with repeating numbers and I would like to find the most frequent but only when there is only one of that.
Your approach seems rather complicated.
Here's how I'd do that:
$numbers = [1, 6, 5, 6, 2, 1, 6, 7, 8]; // positive test case
//$numbers = [1, 6, 5, 6, 2, 1, 6, 7, 8, 1]; // negative test case
$count = array_count_values($numbers); // get count of occurrence for each number
arsort($count); // sort by occurrence, descending
$first = key($count); // get key of first element, because that is the/one
// of the highest number(s)
$count_first = current($count); // get occurrence for first array value
$count_second = next($count); // get occurrence for second array value
if($count_first != $count_second) { // did they occur in different frequencies?
echo $first . ' occurred most in input array.';
}
else {
echo 'input array contained multiple values with highest occurrence.';
}

Answer 2

You could probably perform an array_reduce on the counts to find the max, but because array_reduce does not give you access to the iterable's key, you'd have to perform additional transformation.
Instead, I would recommend you build your own MaxHeap by extending from SplMaxHeap
class MaxHeap extends SplMaxHeap {
public function compare($a, $b) {
if (current($a) < current($b))
return -1;
elseif (current($a) > current($b))
return 1;
else
return 0;
}
}
Then we can use it as such – the answer says [ 7 => 4 ] which means: 7 is the most common number, appearing 4 times
$heap = new MaxHeap();
foreach (array_count_values($numbers) as $n => $count)
$heap->insert([$n => $count]);
print_r($heap->top());
// [ 7 => 4 ]
printf("%d is the most common number, appearing %d times",
key($heap->top()),
current($heap->top())
);
// 7 is the most common number, appearing 4 times
complete script
$numbers = [0, 1, 1, 1, 2, 3, 4, 4, 5, 6, 7, 7, 7, 7, 8, 8, 9];
class MaxHeap extends SplMaxHeap {
public function compare($a, $b) {
if (current($a) < current($b))
return -1;
elseif (current($a) > current($b))
return 1;
else
return 0;
}
}
$heap = new MaxHeap();
foreach (array_count_values($numbers) as $n => $count)
$heap->insert([$n => $count]);
printf("%d is the most common number, appearing %d times",
key($heap->top()),
current($heap->top())
);
revision history
I was unaware of PHP's native array_count_values function. I removed the more complex array_reduce in favor of this super specialised function. Thanks, #CBroe.