使用“array_diff_ukey”比较三个数组的键和值

Question

Can somebody explain, what is 1 and -1 in this code: ($a>$b)?1:-1; ?

I know the Array ( [c] => blue ) is returning because the key c is not exist in $a2 and key_compare_func need to return number smaller, equal or bigger then 0.

But I don't understand, how I get the Array ( [c] => blue ), when the key_compare_func returns 0, 1 and -1:

function myfunction($a,$b) {
    if ($a === $b) {
        return 0;
    }
    return ($a > $b) ? 1 : -1;
}

$a1=array("a"=>"red","b"=>"green","c"=>"blue");
$a2=array("a"=>"blue","b"=>"black","e"=>"blue");

$result=array_diff_ukey($a1,$a2,"myfunction");

Answer 1

As you can see in array-diff-ukey documentation the "key_compare_func" need to return number smaller, equal or bigger then 0. the numbers 1 and -1 are just example for this results.

In your case you can simply use strcmp as it return the same logic.

You have Array ( [c] => blue ) in the return because the key c is not exist in the $a2 array as it say:

Compares the keys from array1 against the keys from array2 and returns the difference. This function is like array_diff() except the comparison is done on the keys instead of the values.

Edited

Specifically in array-diff-ukey you only need the return 0 because that the way this function is decided the keys are the same so in your example you can define it as:

function myfunction($a,$b) {
    if ($a === $b)
        return 0;
    return 1; // or -1 or 3 or -3 **just not 0** 
}

Consider that as the logic behind array-diff-ukey:

array function array-diff-ukey($a1, $a2, $compareFunction) {
    $arr = array(); // init empty array
    foreach($a1 as $key1 => $value1) { // for each key in a1
        $found = false;
        foreach($a1 as $key2 => $value2) { //search for all keys in a2
            if ($compareFunction($key1, $key2) == 0)
                $found = true;  // found a key with the same
        }
        if ($found === false) // add the element only if non is found
            $arr[$key1] = $value1; 
    }
    return $arr;
}