a special array filtering function needed

[pastet89]

HI!
I have an array with dates in the keys and ids in the corresponding values. Some of the values are unique, some of them are repeating. Example:

$arr = (
"1999-01-01" => "2", 
"1999-01-02" => "2", 
"1999-01-03" => "2", 
"1999-01-03" => "3", 
"1999-01-03" => "4", 
"2000-01-03" => "4", 
"2001-01-03" => "4"
);

What I want is if the value is not unique i the array to get only the pair key => value with the latest date, and of course if the value is unique, to get it with its key. So the array I want to get from this is:

$arr_I_need = (
"1999-01-03" => "2", 
"1999-01-03" => "3", 
"2001-01-03" => "4"
);

Can somebody think out a functinon for that... I have been thinking hours, but got to nothing.
10x in advance
PS the date format is yyyy-mm-dd like the one used in strtotime();

[Weedpacket]

I don't see how you can have such an array to begin with: all keys must by definition be unique.

[pastet89]

dont pay attention to this. They are not, but here I wrote them equal for a simplier example. The only equal as I said , are some of the values.

[Weedpacket]

Simplifying an example to the point of absurdity makes it more difficult to answer. It wouldn't have been harder to make sure all the keys were different.

krsort($arr);
$arr = array_unique($arr);