Calculate median and average in PHP

function calculate_median($arr) {
    $count = count($arr); //total numbers in array
    $middleval = floor(($count-1)/2); // find the middle value, or the lowest middle value
    if($count % 2) { // odd number, middle is the median
        $median = $arr[$middleval];
    } else { // even number, calculate avg of 2 medians
        $low = $arr[$middleval];
        $high = $arr[$middleval+1];
        $median = (($low+$high)/2);
    }
    return $median;
}

function calculate_average($arr) {
    $count = count($arr); //total numbers in array
    foreach ($arr as $value) {
        $total = $total + $value; // total value of array numbers
    }
    $average = ($total/$count); // get average value
    return $average;
}

hey! Im uusing your code in a small project of mine (https://github.com/mad-de/PlaCoTo/blob/master/site/resources/functions_calculate_placements.php). Is that alright with you and whats the best way to give you credit?

best wishes and thanks for your coding efforts!

You probably want to sort your array before doing your median calculation.

function calculate_average($arr) {
    return array_sum($arr) / count($arr);
}

There are some missing test cases:

<?php
$test = array(
    array(5,2,1,3,4),
    array(),
    array(1)
);
foreach($test as $arr){
    $count = count($arr);
    sort($arr);
    $mid = floor(($count-1)/2);
    $avg = ($arr)?array_sum($arr)/$count:0;
    $median = ($arr)?($arr[$mid]+$arr[$mid+1-$count%2])/2:0;
    echo 'avg: '.$avg."<br>";
    echo 'median: '.$median."<br>";
}
?>

Or maybe:

<?php
function median($arr){
    if($arr){
        $count = count($arr);
        sort($arr);
        $mid = floor(($count-1)/2);
        return ($arr[$mid]+$arr[$mid+1-$count%2])/2;
    }
    return 0;
}
function average($arr){
    return ($arr) ? array_sum($arr)/count($arr) : 0;
}
$test = array(
    array(5,2,1,3,4),
    array(5,4,2,3,1,6),
    array(),
    array(1),
    array(2,4),
); 
foreach($test as $arr){
    echo 'avg: '.average($arr)."<br>";
    echo 'median: '.median($arr)."<br>";
}
?>

For the scenario where the data set has non-numeric keys (or no elements):

function median(array $arr)
{
    if (0 === count($arr)) {
        return null;
    }

    // sort the data
    $count = count($arr);
    asort($arr);

    // get the mid-point keys (1 or 2 of them)
    $mid  = floor(($count - 1) / 2);
    $keys = array_slice(array_keys($arr), $mid, (1 === $count % 2 ? 1 : 2));
    $sum  = 0;
    foreach ($keys as $key) {
        $sum += $arr[$key];
    }
    return $sum / count($keys);
}

These solutions are nicely understandable but not optimally efficient since they involve fully sorting the array before getting the median out of it.

The optimal efficiency for getting a median is actually O(n) not O(n log n). Have you tried implementing Hoare's Selection algorithm in PHP?
Someone else mentioned it at: http://stackoverflow.com/questions/4201292/on-algorithm-to-find-the-median-of-a-collection-of-numbers

As BramVanroy and other mentioned, array needs to be sorted. In my case I used sort($arr);.

Rewritten from javascript https://stackoverflow.com/a/45309555/2298745

Median PHP:

function median($values) {
  $count = count($values);
  if ($count === 0)  return null;
  asort($values);
  $half = floor($count / 2);
  if ($count % 2) return $values[$half];
  return ($values[$half - 1] + $values[$half]) / 2.0;
}