In PHP how do I remove duplicates in an array of objects where a duplicate is defined as a subset of key-value pairs having the same value [duplicate]

This was fun:

array_multisort(array_column($animArray, 'timestamp'), SORT_DESC, $animArray);

$result = array_intersect_key($animArray,
          array_unique(array_map(function($v) { return $v->dp.'-'.$v->cg; }, $animArray)));

• First, extract the timestamp and sort that array descending, thereby sorting the original array.
• Then, map to create a new array using the dp and cg combinations.
• Next, make the combination array unique which will keep the first duplicate encountered (that's why we sorted descending).
• Finally, get the intersection of keys of the original array and the unique one.

In a function with dynamic properties:

function array_unique_custom($array, $props) {

    array_multisort(array_column($array, 'timestamp'), SORT_DESC, $array);

    $result = array_intersect_key($array,
              array_unique(array_map(function($v) use ($props) {
                  return implode('-', array_map(function($p) use($v) { return $v->$p; }, $props));;
              },
              $array)));

    return $result;
}
$result = array_unique_custom($animArray, ['dp', 'cg']);

Another option would be to sort it ascending and then build an array with a dp and cg combination as the key, which will keep the last duplicate:

array_multisort(array_column($animArray, 'timestamp'), SORT_ASC, $animArray);

foreach($animArray as $v) {
    $result[$v->dp.'-'.$v->cg] = $v;
}

In a function with dynamic properties:

function array_unique_custom($array, $props) {

    array_multisort(array_column($array, 'timestamp'), SORT_ASC, $array);

    foreach($array as $v) {
        $key = implode(array_map(function($p) use($v) { return $v->$p; }, $props));
        $result[$key] = $v;
    }
    return $result;
}
$result = array_unique_custom($animArray, ['dp', 'cg']);

//Create an array with dp and cg values only
$new_arr = [];
foreach($animArray as $key=>$item) {
    $new_arr[] = $item->dp.','.$item->cg;
}
$cvs = array_count_values($new_arr);
$final_array = [];
foreach($cvs as $cvs_key=>$occurences) {
    if ($occurences == 1) {
        $filter_key = array_keys($new_arr, $cvs_key)[0];         
        $final_array[$filter_key] = $animArray[$filter_key];    
    }
}

The final result would be (from your example) in $final_array:

[0] => anim Object
    (
        [qs] => fred
        [dp] => shorts
        [cg] => dino
        [timestamp] => 1590157029399
    )

Some explanation:

//Create a new array based on your array of objects with the attributes dp and cg
//with a comma  between them
$new_arr = [];
foreach($animArray as $key=>$item) {
    $new_arr[] = $item->dp.','.$item->cg;
}
/*
$new_arr now contains:

    [0] => shorts,dino
    [1] => tshirt,bird
    [2] => tshirt,bird
*/

//Use builtin-function array_count_values to get the nr of occurences for 
//each item in an array
$cvs = array_count_values($new_arr);

/*
$cvs would contain:

(
    [shorts,dino] => 1
    [tshirt,bird] => 2
)
*/

//Iterate through the $cvs array.
//Where there are only one occurence (no duplicates)
//create a final array $final_array
$final_array = [];
foreach($cvs as $cvs_key=>$occurences) {
    if ($occurences == 1) {

        /*
        array_keys with second argument $csv_key searches for key with 
        with the key from $cvs-key

        so basically search for:
        shorts,dino and retrieve the key 0 (first element)        
        */
        $filter_key = array_keys($new_arr, $cvs_key)[0];         

        /*
        Add a new item to the $final_array based on the key in
        the original array $animArray
        if you don't want the original key in the new array
        you could just do $final_array[] instead of 
        $final_array[$filter_key]
        */
        $final_array[$filter_key] = $animArray[$filter_key];    
    }
}

You said you would like to have some kind of functionality test different attributes. I believe it would just be making a function/method where you pass in two values to the arguments $attr1 ('dp'?), $attr2('cg'?) or similar.

UPDATE

I had not grasped that you wanted the last value as well. This actually seemed as an easier task. Maybe I am missing something but it was fun to come up with a different approach than other answers :-)

//Create an array with dp and cg values only
$new_arr = [];
foreach($animArray as $key=>$item) {
    $new_arr[] = $item->dp.','.$item->cg;
}

//Sort keys descending order
krsort($new_arr); 

//Because of sending order of keys above, the unique values would return the 
//last item of the duplicates
$new_arr2 = array_unique($new_arr); 

//Switch order of keys back to normal (ascending)
ksort($new_arr2); 

//Create a new array based on the keys set in $new_arr2
//
$final_arr = [];
foreach($new_arr2 as $key=>$item) {
    $final_arr[] = $animArray[$key];
}

The output of $final_arr[] would be (in your example)

Array
(
    [0] => anim Object
        (
            [qs] => fred
            [dp] => shorts
            [cg] => dino
            [timestamp] => 1590157029399
        )

    [1] => anim Object
        (
            [qs] => fred
            [dp] => tshirt
            [cg] => bird
            [timestamp] => 1590117032286
        )

)