Check date ranges (start and end date) for overlap - php

Question

function checkDateOverlap($ranges) {
$res = $ranges[0];
$countRanges = count($ranges);
for ($i = 0; $i < $countRanges; $i++) {
$r1s = $res['start'];
$r1e = $res['end'];
$r2s = $ranges[$i]['start'];
$r2e = $ranges[$i]['end'];
if ($r1s >= $r2s && $r1s <= $r2e || $r1e >= $r2s && $r1e <= $r2e || $r2s >= $r1s && $r2s <= $r1e || $r2e >= $r1s && $r2e <= $r1e) {
$res = array(
'start' => $r1s > $r2s ? $r1s : $r2s,
'end' => $r1e < $r2e ? $r1e : $r2e
);
} else
return false;
}
return $res;
}
// example of returned dates that overlap
$ranges = array(
array('start' => '2014-01-01', 'end' => '2014-01-04'),
array('start' => '2014-01-05', 'end' => '2014-01-10'),
array('start' => '2014-01-04', 'end' => '2014-01-07')
);
//example of failure
$ranges2 = array(
array('start' => '2014-01-01', 'end' => '2014-01-04'),
array('start' => '2014-01-05', 'end' => '2014-01-10'),
array('start' => '2014-01-11', 'end' => '2014-01-17')
);
var_dump(checkDateOverlap($ranges));
The following is what I was attempting to check intersection of date ranges. In the array "ranges1" this example has overlapping dates. It should return the dates. In array $ranges2, this should pass as no intersecting dates.
Now the weird thing is the start and end date can be the exact same, so you could make an entry for just a single day. I've tried many things, and I'm stumped.
I believe there needs to be another for loop, but regardless I am not getting success.
Here was another go I had:
<?php
// pass your ranges to this method and if there is a common intersecion it will
// return it or false
function checkDateOverlap($ranges){
$res = $ranges[0];
$countRanges = count($ranges);
for ($i = 0; $i < count($countRanges); $i++) {
for($j = $i+1; $j < count($countRanges); $j++) {
$r1s = $res['start'];
$r1e = $res['end'];
$r2s = $ranges[$i]['start'];
$r2e = $ranges[$i]['end'];
if (($r1s >= $r2e && $r2s <= $r1e)) {
$res[] = array(
'start' => $r1s > $r2s ? $r1s : $r2s,
'end' => $r1e < $r2e ? $r1e : $r2e
);
} else
return false;
}
}
return $res;
}
// example
$ranges = array(
array('start' => '2014-01-04', 'end' => '2014-01-05'),
array('start' => '2014-01-06', 'end' => '2014-01-10'),
array('start' => '2014-01-11', 'end' => '2014-01-13')
);
echo "<pre>";
var_dump(checkDateOverlap($ranges));
echo "</pre>";
Any advice greatly appreciated.

Answer 1

$ranges = array(
array('start' => new DateTime('2014-01-01'), 'end' => new DateTime('2014-01-05')),
array('start' => new DateTime('2014-01-06'), 'end' => new DateTime('2014-01-06')),
array('start' => new DateTime('2014-01-07'), 'end' => new DateTime('2014-01-07')),
);
function intersects($lhs, $rhs) {
// Note that this function allows ranges that "touch",
// eg. one pair starts at the exact same time that the other ends.
// Adding less "or equal to" will allow same start date
return !($lhs['start'] > $rhs['end'] || $lhs['end'] < $rhs['start']);
}
function checkDates($ranges) {
// Comparison loop is of size n•log(n), not doing any redundant comparisons
for($i = 0; $i < sizeof($ranges); $i++) {
for($j = $i+1; $j < sizeof($ranges); $j++) {
if(intersects($ranges[$i], $ranges[$j])) {
echo "Date {$i} intersects with date {$j}\n";
}
}
}
}
checkDates($ranges);
I've attached my working code sample to hopefully help someone else in the future looking for the same solution. This will print the arrays that intersect.

Answer 2

If you use usort to first sort the dates, the work gets a lot easier. The following can be optimized a lot, but it is done step-by-step make it easier to understand.
//The date comparison function, sort on start and then on end
function cmp($a, $b)
{
if($a['start']<$b['start']) return -1;
if($a['start']>$b['start']) return 1;
if($a['end']<$b['end']) return -1;
if($a['end']>$b['end']) return 1;
return 0; // start=start and end=end
}
$ranges = array(
array('start' => '2014-01-01', 'end' => '2014-01-04'),
array('start' => '2014-01-05', 'end' => '2014-01-10'),
array('start' => '2014-01-04', 'end' => '2014-01-07')
);
usort($ranges, 'cmp'); // Sort the dates
$output = array();
for($i=0; $i<sizeof($ranges); $i++)
{
$endindex = $i; // The index containing the proper 'end' value
for($j=$i+1; $j<sizeof($ranges); $j++)
{
if($ranges[$endindex]['start'] == $ranges[$j]['start']) // Overlap
$endindex = $j;
elseif($ranges[$endindex]['end']>=$ranges[$j]['start']) // Overlap
$endindex = $j;
}
$output[] = array('start' => $ranges[$i]['start'], 'end' => $ranges[$endindex]['end']);
// Break the rules by hard-setting $i from the for loop - it works great in this case
$i = $endindex;
}
print_r($output);
It works for your example. If you have other rules that must be used, hopefully you can adjust this code.

Answer 3

Here are some remarks:
- You do not check the validity of the date formed by 'start' and 'end'.
- Why do you not convert the dates to timestamp ?
-> It's more easier and faster to compare integer value instead of string ?
Why do you not use PHP DateTime and DateInterval Objects ?
http://php.net/manual/en/book.datetime.php