Create date ranges from consecutive dates in an array

I have arrays of dates in Y-m-d format that may be any combination of ten set dates that are zero, one, or more days apart.

e.g. Here is a possible full set:

[
    '2011-01-01',
    '2011-01-02',
    '2011-01-03',
    '2011-01-04',
    '2011-01-05',
    '2011-01-06',
    '2011-01-07',
    '2011-01-08',
    '2011-01-09',
    '2011-01-10'
]

The arrays that are created from that set can be any combination of consecutive or gapped dates.

I currently have them printing pretty much as they're returned. e.g. here's another possible data set:

[
    '2011-01-02',
    '2011-01-03',
    '2011-01-04',
    '2011-01-08',
]

(What's actually printed is more like "Friday, Jan. 2…", but we'll stick with the simple date string.)

I'd like to condense it so that if there are three or more consecutive days, those become a range, e.g the above example would become:

[
    '2011-01-02 to 2011-01-04',
    '2011-01-08',
]

which would eventually become:

[
    'Sunday, Jan. 2 - Tuesday, Jan. 4',
    'Saturday Jan. 8',
]

Is there a way to loop through and consolidate consecutive dates as ranged date strings?

Bit of a quick answer so sorry about the lack of implementation but assuming you are using 5.3 and the dates are ordered chronologically, you could convert each date to a DateTime object (if they aren't already) and then iterate over the array using DateTime::diff() to generate a DateInterval object which you could use to compare the current date in the iteration with the last. You could group your consecutive dates into sub arrays and use shift() and pop() to get the first and last days in that sub array.

EDIT

I had a think about this. Pretty rough and ready implementation follows, but it should work:

// assuming a chronologically
// ordered array of DateTime objects 

$dates = array(
    new DateTime('2010-12-30'), 
    new DateTime('2011-01-01'), 
    new DateTime('2011-01-02'), 
    new DateTime('2011-01-03'), 
    new DateTime('2011-01-06'), 
    new DateTime('2011-01-07'), 
    new DateTime('2011-01-10'),
);

// process the array

$lastDate = null;
$ranges = array();
$currentRange = array();

foreach ($dates as $date) {    

    if (null === $lastDate) {
        $currentRange[] = $date;
    } else {

        // get the DateInterval object
        $interval = $date->diff($lastDate);

        // DateInterval has properties for 
        // days, weeks. months etc. You should 
        // implement some more robust conditions here to 
        // make sure all you're not getting false matches
        // for diffs like a month and a day, a year and 
        // a day and so on...

        if ($interval->days === 1) {
            // add this date to the current range
            $currentRange[] = $date;    
        } else {
            // store the old range and start anew
            $ranges[] = $currentRange;
            $currentRange = array($date);
        }
    }

    // end of iteration... 
    // this date is now the last date     
    $lastDate = $date;
}

// messy... 
$ranges[] = $currentRange;

// print dates

foreach ($ranges as $range) {

    // there'll always be one array element, so 
    // shift that off and create a string from the date object 
    $startDate = array_shift($range);
    $str = sprintf('%s', $startDate->format('D j M'));

    // if there are still elements in $range
    // then this is a range. pop off the last 
    // element, do the same as above and concatenate
    if (count($range)) {
        $endDate = array_pop($range);
        $str .= sprintf(' to %s', $endDate->format('D j M'));
    }

    echo "<p>$str</p>";
}

Outputs:

Thu 30 Dec
Sat 1 Jan to Mon 3 Jan
Thu 6 Jan to Fri 7 Jan
Mon 10 Jan