comparing two arrays in php - php

Question

I use this code :
$new = array(
"123" => "a",
"456" => "b"
);
$old = array(
"123" => "a",
"456" => "b"
);
then the $new array become like this:
$new = array(
"456" => "b",
"123" => "c",
"789" => "e"
);
as you see the count of $new array increased and the order of elements changed and the value at key 123 also changed. I need to compare the $new array against the $old array and catch only the change made on the value at key 123 without caring about the order and the count of elements. I tried:
$result = array_diff( $new, $old );
print_r( $result );
output :
Array ( [123] => c [789] => e )

Answer 1

UPDATE. quite confusing. now I think we got it
$old = array(
"123" => "a",
"456" => "b"
);
$new = array(
"456" => "b",
"123" => "c", // catch this (element in old array that is changed)
"789" => "e"
);
$new2 = array();
foreach ($new as $key => $new_val)
{
if (isset($old[$key])) // belongs to old array?
{
if ($old[$key] != $new_val) // has changed?
$new2[$key] = $new[$key]; // catch it
}
}
// output $new2:
array (
123 => 'c',
)

Answer 2

You first of all want to have those elements of $new that are changed compared to $old (see array_diff_assoc):
$changed = array_diff_assoc($new, $old);
Of that result you want to have only those elements that have their key in $old (see array_intersect_key):
$result = array_intersect_key($changed, $old);
And that's it. You can wrap that into each other if it helps:
array_intersect_key(array_diff_assoc($new, $old), $old);
Result is:
array(1) {
[123] =>
string(1) "c"
}
Full example (Demo):
$old = array(
"123" => "a",
"456" => "b"
);
$new = array(
"456" => "b",
"123" => "c", // catch only the change made on the value at key 123
"789" => "e"
);
$changed = array_diff_assoc($new, $old);
$result = array_intersect_key($changed, $old);
var_dump($result);
Just a final note: There are many array functions in PHP. It's worth to go through the list and look what is fitting because most often you only need one or two of them to get things like these done.

Answer 3

You use this code for your requirements
<?php
function key_compare_func($key1, $key2)
{
if ($key1 == $key2)
return 0;
else if ($key1 > $key2)
return 1;
else
return -1;
}
$array1 = array('blue' => 1, 'red' => 2, 'green' => 3, 'purple' => 4);
$array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan' => 8);
var_dump(array_intersect_ukey($array1, $array2, 'key_compare_func'));
?>