使用usort（PHP）对数组中的2个字段ASC进行排序

Question

i have a textfile with this content (id;date;user):

8559;2014-06-13;Carlos
8584;2014-06-23;1A Auto
8398;2014-06-02;LRDream
7738;2014-05-19;Felicitia Motors
8475;2014-06-06;Motori
8331;2014-06-30;Otto Burner
8521;2014-06-24;Mirage
3699;2014-06-30;LR DMJ
8050;2014-05-19;1A Auto
7428;2014-05-20;Carlos

Goal is to output this data sorted by 1) month and 2) username.

<?

$data = file("data.csv");

foreach ($data as $value)
{
$bla=explode(";",$value);
$new[$bla[0]]['date']=substr($bla[1],0,-3);
$new[$bla[0]]['user']=$bla[2];
}

function comp($a, $b)
{ if ($a['date'] == $b['date']) { return $a['user'] - $b['user']; }
return strcmp($a['date'], $b['date']);
} 
usort($new, 'comp');

foreach ($new as $value)
{
echo $value['date']." - ".$value['user']."<br>";
}

?>

This sorts the months correctly but the users are not really sorted:

2014-05 - Carlos
2014-05 - Felicitia Motors
2014-05 - 1A Auto <---
2014-06 - LR DMJ
2014-06 - Mirage
2014-06 - Motori
2014-06 - LRDream <---
2014-06 - Carlos <---
2014-06 - Otto Burner
2014-06 - 1A Auto <---

What wrong with the code?

Thanks! NBG

Answer 1

That's because you are not comparing the usernames -- you are subtracting them numerically, which gives totally inappropriate results (see string conversion to numbers).

Replace return $a['user'] - $b['user'] with return strcmp($a['user'], $b['user']) to get the expected result.

Shameless self-promotion: You could also consider using the handy sorting technique I give here to get the correct result with much more appealing code:

usort($new, make_comparer('date', 'user'));