Calculating the median & average values of an array with PHP

Here's a couple of handy little PHP functions I wrote to calculate the median & average values of an array of numbers.

The median value is literally the middle number, this is useful in many instances, often used in real estate statistics for example, as it can help show what people are paying for a home, without the value being skewed by a few low-end or high-end transactions.

Take the following home sales numbers for example;

• $100,000
• $120,000
• $150,000
• $157,000
• $180,000
• $198,000
• $220,000
• $1,450,000

The average of those home sale prices would be $321,875, we can see that the high-end home price has dramatically skewed the true price most people are paying. Now using the median calculation, we can determine that the median price would be $168,500. The functions below don't do any error checking, so you may want to add checks to verify an array is being passed, whether the values are numeric, etc.

<?php
function calculate_median($arr) {
    sort($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;
}

$home_values_array = array("100000", "120000", "150000", "157000", "180000", "198000", "220000", "1450000");

$median_home_value = calculate_median($home_values_array);
echo '<p>Median home value: $'.number_format($median_home_value).'<br />';
$average_home_value = calculate_average($home_values_array);
echo 'Average home value: $'.number_format($average_home_value).'</p>';
?>

The resulting output from the above would be;

Median home value: $168,500
Average home value: $321,875