detect where elements in array moved - php

Question

I have to be able to detect all changes in a "guild" (like an activity feed), with new and old data. The data is presented in this fashion, as an array:
{"GUILDMASTER":["foo"],"OFFICER":["bar","baz"],"MEMBER":["foobar","foobaz"]}
I need to detect if, for example, "bar" moves from his current rank down one (to "MEMBER"), it will output an array something like this:
[{"user":"bar","was_found_in":"OFFICER","now_found_in":"MEMBER"}]
What I currently have, below, only detects if a member has joined of left, is there any way to extend this to fulfill what I want it to?
function compareThem($a, $b) {
$flat_new = call_user_func_array('array_merge', $a);
$flat_old = call_user_func_array('array_merge', $b);
$rm = array();
if($flat_new != $flat_old) {
$new_old = array_diff($flat_new, $flat_old);
$old_new = array_diff($flat_old, $flat_new);
$diff = array_merge($new_old, $old_new);
foreach ($diff as $key => $value) {
if(in_array($value, $flat_new) && !in_array($value, $flat_old)) {
$rm[] = array("new"=>true, "left"=>false, "user"=>$value);
} else if(in_array($value, $flat_old) && !in_array($value, $flat_new)) {
$rm[] = array("new"=>false, "left"=>true, "user"=>$value);
}
}
}
return $rm;
}
$new = array("GUILDMASTER" => array("foo"), "OFFICER" => array("bar", "baz"), "MEMBER" => array("foobar", "foobaz"));
$old = array("GUILDMASTER" => array("foo"), "OFFICER" => array("bar", "baz"), "MEMBER" => array("foobar"));
compareThem($new,$old) // will output [{"new":true,"left":false,"user":"foobaz"}]

Answer 1

You can do this. It detects additions, deletions, and modifications:
// your array before the change
$before = ["GUILDMASTER" => ["foo"], "OFFICER" => ["bar","baz"], "MEMBER" => ["foobar","foobaz"]];
// your array after the change (foo was moved from GUILDMASTER to OFFICER)
$after = ["GUILDMASTER" => [], "OFFICER" => ["bar","baz", "foo"], "MEMBER" => ["foobar","foobaz"]];
// create lookup table to check the position a person previously held
$positions_before = [];
foreach($before as $position => $people) {
foreach($people as $person) {
$positions_before[$person] = $position;
}
}
// scan new positions...
$changes = [];
foreach($after as $position => $people) {
foreach($people as $person) {
// track when a new person is added (they wont be in the table)
if(!isset($positions_before[$person])) {
$changes[] = ["user" => $person, "was_found_in" => "DIDNT_EXIST", "now_found_in" => $position];
// track when a change is detected (different value than table)
}elseif($positions_before[$person] != $position) {
$changes[] = ["user" => $person, "was_found_in" => $positions_before[$person], "now_found_in" => $position];
}
// remove this person from the table after parsing them
unset($positions_before[$person]);
}
}
// anyone left in the lookup table is in $before and $after
// so track that they were removed/fired
foreach($positions_before as $person => $position) {
$changes[] = ["user" => $person, "was_found_in" => $position, "now_found_in" => "REMOVED"];
}
print_r($changes);
outputs [user] => foo [was_found_in] => GUILDMASTER [now_found_in] => OFFICER