intersection of array keys

[ednark]

ok i have what is basically a hashtable mapping an item to its id

$list1 = array(
    $item1_id  => $item1_object,
    $item2_id  => $item2_object,
    $item3_id  => $item3_object,
    $item4_id  => $item4_object
);

$list2 = array(
    $item5_id  => $item5_object,
    $item6_id  => $item6_object,
    $item7_id  => $item7_object,
    $item1_id  => $item1_object
);

i want to see if any items in $list1 are also in $list2
i want to check that ( L1 intersect L2 == empty_set )

whats the best way to do this... i have some ideas but thought this would be something neat for the forum to think about

this is more an exercise in efficiency than in do-ability

[trooper]

The function in_array() will do that for you. Take a look at it
HTH

GM

Originally posted by ednark
ok i have what is basically a hashtable mapping an item to its id

$list1 = array(
    $item1_id  => $item1_object,
    $item2_id  => $item2_object,
    $item3_id  => $item3_object,
    $item4_id  => $item4_object
);

$list2 = array(
    $item5_id  => $item5_object,
    $item6_id  => $item6_object,
    $item7_id  => $item7_object,
    $item1_id  => $item1_object
);

i want to see if any items in $list1 are also in $list2
i want to check that ( L1 intersect L2 == empty_set )

whats the best way to do this... i have some ideas but thought this would be something neat for the forum to think about

this is more an exercise in efficiency than in do-ability [/B]

[Weedpacket]

Hm; you say "array keys" in the heading: does this mean that the intersection of ('a'=>42) and ('b'=>42) should be empty? What would be the intersection of ('a'=>42) and ('a'=>1701) be? array_intersect()'s answers are respectively ('a'=>42) and () - it intersects on the value and keeps the first key.

If you're wanting an array of keys that appear in both lists, then I guess array_interset(array_keys($array1), array_keys($array2)) would be the most straightforward, but I haven't thunked enough yet about reattaching values.

[ednark]

sigh... RTFM ednark!!!!

ok.. well let this be a lesson for me...

the first thing i did was search for a function called array_intersect or some derevation of

though i didn't find anything.

mots likley i didn"t spelll arrray_intesrect corectelly

and i never just read through the list of array functions

i will do more finger stretches before bothering the forum..

[man]count[/man]( [man]array_intersect[/man]( [man]array_keys/man, [man]array_keys/man ) ) == 0

was what i was looking for...

errr.. what i mean was.. this was a test just to see if the forum was on the ball

[Weedpacket]

Oh, okay. Actually, I did think of a more interesting problem that grew from thinking about it: Given an array $array, and an array $keys; what are the values in $array, corresponding to the keys given in $keys?

It's easy enough to write a quick loop for the job:

$default='';
$result=array();
foreach($keys as $key)
   $result[$key] = isset($array[$key]) ? $array[$key] : $default;

But it seems like a generalisation of array_slice() worthy of coding into that function.

array_slice(array array, array keys [mixed default])