PHP array group sorting example code

There is the following PHP array, the contents of the array:

$list = array(
 array(2,3,5),
 array(2,5,24),
 array(3,8,6),
 array(3,2,10) ,
 array(4,7,20),
 array(4,1,15),
 array(6,4,10),
 array(7,9,20),
 );

For the convenience of expression, I call the three columns of numbers respectively, the three columns of ABC Requirements: By default, column A is the main sorting method. If columns A are the same, the same elements are sorted in column C in reverse order. Column B does not actually participate in sorting, but it is useful in practical applications, so it is also written. method one:

$a = $c = array();
foreach($list as $val){
 $a[] = $val[0]; //column a
 $c [] = $val[2]; //Column c
}
//Install column a in ascending order, and then install column b in descending order, similar to sql, orderby a asc,b desc
array_multisort($a,SORT_ASC, $c, SORT_DESC , $list);
print_r($list);

Method 2:

for($j=0;$j for($i=count($list)-1;$i>$j ;$i--){
 if($list[$i][0] == $list[$i-1][0] && $list[$i][2] > $list[$i- 1][2])
 list($list[$i],$list[$i-1]) = array($list[$i-1],$list[$i]);
 }
}