I had a situation where I needed to obtain the next available key in an array, which is the highest+1.
For example, if the array is $data=['1'=>'something,'34'=>'something else'] then I needed to calculate 35 to add a new element to the array that had a key higher than any of the others. In the case of an empty array I needed 1 as next available key.
This is the solution that worked:
$highest = 0;
foreach($data as $idx=>$dummy)
{
if($idx > $highest)$highest=$idx;
}
$highest++;
It will work in all cases, empty array or not. If you only need to find the highest key rather than highest key + 1, delete the last line. You will then get a value of 0 if the array is empty.