Compare the keys and values of three arrays with "array_diff_ukey" - php

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;
}

Answer 2

If ($a>$b) is true (right after the ?) - you return 1. else (right after the :) will return -1.
It's a short way of writing this:
if ($a>$b) {
return 1;
} else {
return -1;
}

Answer 3

It is the ternary operator in PHP. You can say it as shorthand If/Else. Here is an example:
/* most basic usage */
$var = 5;
$var_is_greater_than_two = ($var > 2 ? true : false); // if $var greater than 2
// return true
// else false
If it is being difficult for you to understand, you can change it with:
if ($a===$b)
{
return 0;
}
else if($a > $b)
{
return 1;
}
else
{
return -1;
}