Question

How can I determine if one array is a subset of another (all elements in the first are present in the second)?

 $s1 = "string1>string2>string3>string4>string5>string6>";
 $arr1 = explode(">", $s1);
 $s2 = "string1>string4>string5";
 $arr2 = explode(">", $s2);

 $isSubset = /* ??? */

Answer 1

If you start from strings, you could check strstr($fullString,$subsetStr);. But that’ll only work when all chars have the same order: 'abcd','cd' will work, but 'abcd','ad' won’t.

But instead of writing your own, custom, function you should know that PHP has TONS of array functions, so its neigh on impossible that there isn’t a std function that can do what you need it to do. In this case, I’d suggest array_diff:

$srcString = explode('>','string1>string2>string3>string4>string5');
$subset = explode('>','string3>string2>string5');
$isSubset = array_diff($subset,$srcString);
//if (empty($isSubset)) --> cf comments: somewhat safer branch:
if (!$isSubset)
{
    echo 'Subset';
    return true;
}
else
{
    echo 'Nope, substrings: '.implode(', ',$isSubset).' Didn\'t match';
    return false;
}