Question

I’ve got an array that uses UNIX timestamps for array keys. The array will typically hold data for anywhere from 15 minutes to maybe an hours worth of time, however there are only entries for seconds that have data.

Most of the data will be spread out, there will be occasional spans of data for consecutive seconds though. What I’d like to do, is retrieve the first and last second of the longest consecutive span of seconds in the array.

If I have this array

Array
(
    [1276033307] => 119.0
    [1276033331] => 281.8
    [1276033425] => 28.2
    [1276033431] => 88.2
    [1276033432] => 196.2
    [1276034207] => 205.5
    [1276034226] => 73.8
    [1276034227] => 75.8
    [1276034228] => 77.8
    [1276034230] => 79.8
)

I would either need the keys 1276034226 and 1276034228, or the following array returned.

Array
(
    [1276034226] => 73.8
    [1276034227] => 75.8
    [1276034228] => 77.8
)

Answer 1

This code does it in a single loop (i.e. is a Greedy algorithm):

$array = array(
    1276033307 => 119.0,
    1276033331 => 281.8,
    1276033425 => 28.2,
    1276033431 => 88.2,
    1276033432 => 196.2,
    1276034207 => 205.5,
    1276034226 => 73.8,
    1276034227 => 75.8,
    1276034228 => 77.8,
    1276034230 => 79.8,
);

$long_arr = array();
$curr_arr = array();
$last_key = -1;

foreach($array as $k => $v) {
    if ($k != $last_key + 1) {
        $curr_arr = array();
    }
    $curr_arr[$k] = $v;
    if (count($curr_arr) > count($long_arr)) {
        $long_arr = $curr_arr;
    }
    $last_key = $k;
}

print_r($long_arr);