order dates upcoming

so i build an array several dates. birthdays, anniversaries, holidays. i'd method array duty next, radically arrange october september (wrapping unbroken year)

so array

$a = ([0]=>"1980-04-14", [1]=>"2007-06-08", 
  [2]=>"2008-12-25", [3]=>"1978-11-03")

i'd arrange arranged

$a = ([0]=>"1978-11-03", [1]=>"2008-12-25", 
  [2]=>"1980-04-14", [3]=>"2007-06-08")

because november 'event' occur unbroken (based being october right now).

i'm perplexing usort where cmp duty

function cmp($a, $b)
{
  $a_tmp = split("-", $a);
  $b_tmp = split("-", $b);
  relapse strcmp($a_tmp[1], $b_tmp[1]);
} 

i am certain cgange preferred effect.