Comparing multiple different dates and getting the average in PHP

I use a function called count_days($date1,$date2) that counts the number of days between two dates. But, my question is: the dates come from the DB, in an array like:

Array (
  [imac] => Array (
    [0] => 2002-10-10
    [1] => 2003-11-22
    [3] => 2004-11-10
  )
  [iphone] => Array (
    [0] => 2007-09-11
    [1] => 2008-05-12
    [2] => 2009-0开发者_开发知识库6-14
    [3] => 2010-06-05
  )
)

As you can see the products may have a different number of subarrays.

I want to count the days between the first and the next date (and so on!) and then get the average of days.

The DateInterval class is great for this kind of date arithmetic. You can use DateTime::add, DateTime::subtract and DateTime::diff to work with them.

<?php

$types = array(
    'imac' => array ('2002-10-10', '2003-11-22', '2004-11-10'),
    'iphone' => array ( '2007-09-11', '2008-05-12', '2009-06-14', '2010-06-05'),
);

$typeIntervals = array();
$typeAverage = array();
foreach ($types as $type=>$dates) {
    $last = null;
    $typeIntervals[$type] = array();
    foreach ($dates as $date) {
        $current = new DateTime($date);
        if ($last) {
            $interval = $current->diff($last);
            $typeIntervals[$type][] = $interval->days;
        }
        $last = $current;
    }
    $typeAverage[$type] = array_sum($typeIntervals[$type]) / count($typeIntervals[$type]);
}

print_r(typeIntervals);
print_r($typeAverage);

This will output:

Array (
    [imac] => Array (
            [0] => 408
            [1] => 354
        )
    [iphone] => Array (
            [0] => 244
            [1] => 398
            [2] => 356
        )
)
Array (
    [imac] => 381
    [iphone] => 332.66666666667
)

try smth like this ( not tested )

$lastDate = $dbArray[0][0];
    $daysArray = array();
    foreach ( $dbArray as $value )
    {
        if ( is_array($value) )
        {
            foreach ( $value as $v )
            {
                $daysArray[] = count_days($lastDate, $v);
                $lastDate = $v;
            }
        } else {
            //not an array check if it's a date and test it here
        }
    }
    $average = array_sum($daysArray)/count($daysArray);