$arr1=array('a_b','c_d','b_a','d_c');
$arr2=array('a_b','c_d','b_a','d_c');

条件:

a_b==b_a;
c_d==d_c;

需求:想得到无重复的数组:

$newArr=array('a_b','a_c');

解法:

$newArr=array();
foreach($arr2 as $key=>$value){
    $ceilArr=explode("_",$value);
    $str=$ceilArr[1].'_'.$ceilArr[0];
    if( in_array("$value",$arr1) && in_array("$str",$arr1) ){
        //echo array_search("$str",$arr1);echo '<br />';
                $newArr[]=$value;

        unset($arr1[array_search("$value",$arr1)]);
        unset($arr1[array_search("$str",$arr1)]);

    }
}

echo '<pre />';
print_r($newArr);
echo count($newArr);

The end