PHP: Condense array of similar strings into one merged array

Question

Hi everyone.

Working with an array of dates (opening times for a business). I want to condense them to their briefest possible form.

So far, I started out with this structure

Array
(
    [Mon] => 12noon-2:45pm, 5:30pm-10:30pm
    [Tue] => 12noon-2:45pm, 5:30pm-10:30pm
    [Wed] => 12noon-2:45pm, 5:30pm-10:30pm
    [Thu] => 12noon-2:45pm, 5:30pm-10:30pm
    [Fri] => 12noon-2:45pm, 5:30pm-10:30pm
    [Sat] => 12noon-11pm
    [Sun] => 12noon-9:30pm
)

What I want to achieve is this:

Array
(
    [Mon-Fri] => 12noon-2:45pm, 5:30pm-10:30pm
    [Sat] => 12noon-11pm
    [Sun] => 12noon-9:30pm
)

I've tried writing a recursive function and have managed to output this so far:

Array
(
    [Mon-Fri] => 12noon-2:45pm, 5:30pm-10:30pm
    [Tue-Fri] => 12noon-2:45pm, 5:30pm-10:30pm
    [Wed-Fri] => 12noon-2:45pm, 5:30pm-10:30pm
    [Thu-Fri] => 12noon-2:45pm, 5:30pm-10:30pm
    [Sat] => 12noon-11pm
    [Sun] => 12noon-9:30pm
)

Can anybody see a simple way of comparing the values and combining the keys where they're similar? My recursive function is basically two nested foreach() loops - not very elegant.

Thanks, Matt

EDIT: Here's my code so far, which produces the 3rd array above (from the first one as input):

$last_time = array('t' => '', 'd' => ''); // blank array for looping
$i = 0;

foreach($final_times as $day=>$time) {

    if($last_time['t'] != $time ) { // it's a new time

        if($i != 0) { $print_times[] = $day . ' ' . $time; } 
        // only print if it's not the first, otherwise we get two mondays

    } else { // this day has the same time as last time

        $end_day = $day;

        foreach($final_times as $day2=>$time2) {

            if($time == $time2) {
                $end_day = $day2;
            }

        }

        $print_times[] = $last_time['d'] . '-' . $end_day . ' ' . $time;

    }

$last_time = array('t' => $time, 'd' => $day);
$i++;

}

Answer 1

I don't think there is a particularly elegant solution to this. After much experimenting with the built in array_* functions trying to find a nice simple solution, I gave up and came up with this:

$lastStart = $last = $lastDay = null;
$new = array();

foreach ($arr as $day => $times) {
 if ($times != $last) {
  if ($last != null) {
   $key = $lastStart == $lastDay ? $lastDay : $lastStart . '-' . $lastDay;
   $new[$key] = $last;
  }
  $lastStart = $day;
  $last = $times;
 }
 $lastDay = $day;
}

$key = $lastStart == $lastDay ? $lastDay : $lastStart . '-' . $lastDay;
$new[$key] = $last;

It only uses one foreach loop as opposed to your two, as it keeps a bunch of state. It'll only merge adjacent days together (i.e., you won't get something like Mon-Tue,Thu-Fri if Wednesday is changed, you'll get two separate entries).

Answer 2

I'd approach it by modelling it as a relational database:

day      start        end
1        12:00        14:45
1        17:30        22:30
...

Then its fairly easy to reduce - there are specific time intervals:

SELECT DISTINCT start, end FROM timetable;

And these will occur on specific days:

SELECT start, end, GROUP_CONCAT(day) ORDER BY day SEPERATOR ',' FROM timetable GROUP BY start,end

(this uses the MySQL-only 'group_concat' function - but the method is the same where this is not available) would give:

12:00    14:45  1,2,3,4,5
17:30    22:30  1,2,3,4,5
12:00    23:00  6
12:00    21:30  7

Then it's fairly simple to work out consecutive date ranges from the list of days.

C.