I have looked at the php documentation, tutorials online and none of them how usort is actually working. I have an example i was playing with below.
$data = array(
array('msg' => 'some text','month' => 11,'level' => 10),
array('msg' => 'some text','month' => 5,'level' => 10),
array('msg' => 'some text','month' => 8,'level' => 10),
array('msg' => 'some text','month' => 12,'level' => 10),
array('msg' => 'some text','month' => 2,'level' => 10),
array('msg' => 'some text','month' => 3,'level' => 10),
array('msg' => 'some text','month' => 4,'level' => 10),
array('msg' => 'some text','month' => 7,'level' => 10),
array('msg' => 'some text','month' => 10,'level' => 10),
array('msg' => 'some text','month' => 1,'level' => 10),
array('msg' => 'some text','month' => 6,'level' => 10),
array('msg' => 'some text','month' => 9,'level' => 10)
);
I wanted to be able to sort the months from 12 to 1 (since their unorganized) through some help this was the solution
function cmp($a, $b)
{
if ($a["month"] == $b["month"])
{
return 0;
}
return ($a["month"] < $b["month"]) ? -1 : 1;
}
usort($data, "cmp");
but i dont understand how the function cmp sorts the array. i tried printing out each variable $a and $b like this:
function cmp($a, $b)
{
echo "a: ".$a['month']."<br/>";
echo " b: ".$b['month']."<br/>";
echo "<br/><br/>";
}
and the output was
a: 3
b: 5
a: 9
b: 3
a: 3
b: 8
a: 6
b: 3
a: 3
b: 12
a: 1
b: 3
a: 3
b: 2
a: 10
b: 3
a: 3
b: 11
a: 7
b: 3
a: 4
b: 3
a: 12
b: 2
a: 5
b: 12
a: 12
b: 11
a: 8
b: 12
a: 5
b: 8
a: 2
b: 11
a: 6
b: 9
a: 7
b: 6
a: 6
b: 4
a: 10
b: 6
a: 1
b: 6
a: 9
b: 4
a: 7
b: 1
a: 10
b: 7
it makes no sense to how the sort is working and why cmp($a, $b) is used. i have tried to print out all its processes as you can see but have not come to any solution to how it all works..
thanks
The function cmp
itself doesn't do the sorting. It just tells usort
if a value is smaller, equal or greater than another value. E.g. if $a = 5
and $b = 9
it will return 1 to indicate that the value in $b
is greater than the one in $a
.
Sorting is done by usort
.