PHP は 2 つの配列のキー名を比較し、交差関数 array_intersect_key() を返します。

<?php
$a1=array("a"=>"red","b"=>"green","c"=>"blue");
$a2=array("a"=>"red","c"=>"blue","d"=>"pink");

$result=array_intersect_key($a1,$a2);
print_r($result);
?>

array_intersect_key(array1,array2,array3...)

<?php
$a1=array("red","green","blue","yellow");
$a2=array("red","green","blue");

$result=array_intersect_key($a1,$a2);
print_r($result);
?>

<?php
$a1=array("a"=>"red","b"=>"green","c"=>"blue");
$a2=array("c"=>"yellow","d"=>"black","e"=>"brown");
$a3=array("f"=>"green","c"=>"purple","g"=>"red");

$result=array_intersect_key($a1,$a2,$a3);
print_r($result);
?>

<?php
 $array1  = array( &#39;one&#39;   =>  1 ,  &#39;two&#39;   =>  2 ,  &#39;three&#39;   =>  3 ,  &#39;five&#39;  =>  4 ); 
$array2  = array( &#39;six&#39;  =>  5 ,  &#39;one&#39;  =>  6 ,  &#39;five&#39;  =>  7 ,  &#39;ten&#39;    =>  8 );
 var_dump ( array_intersect_key ( $array1 ,  $array2 ));
?>