Remove key-value pairs found in subsequent rows while looping 2d array

Question

I have a two dimensional array with indexed rows of associative elements. I need to retain the first occurring key-value pairs while iterating from the start of the array to the end.

Input:

$ar = [
     ["a" => "b", "c" => "d", "h" => "e"],
     ["a" = "b", "f" => "g"]
];

I've tried array_unique(), but it's not suitable for thistask.

Expected result:

[
     ["a" => "b", "c" => "d", "h" => "e"],
     ["f" => "g"]
]

---

Another example:

$ar = [
    ["a" => "b", "b" => "w", "c" => "e"!],
    ["c" => "g", "a" => "b"]
];

Expected result:

[
    ["a" => "b", "b" => "w", "c" => "e"],
    ["c" => "g"]
]

Answer 1

• In this scenario, you need to be careful with duplicate keys yet different values. So match to remove duplicates has to be on combination of both key and value.

• To do this, we can collect all keys in an array say $map and have all values visited for this keys inside that key array.

• Now, we can just do an in_array check to get hold of whether we got some key-value pair like this before or not.

Snippet:

$arr = [
    [
        'a' => 'b',
        'c' => 'd',
        'h' => 'e'
    ],
    [
        'a' => 'b',
        'f' => 'g',
        'c' => 'f'
    ],
    [
        'a' => 'd',
        'c' => 'd'
    ]
];

$map = [];
foreach($arr as $index => $data){
    foreach($data as $key => $value){
        if(!isset($map[$key])) $map[$key] = [];
        if(in_array($value,$map[$key])) unset($arr[$index][$key]);
        else $map[$key][] = $value;
    }
}

print_r($arr);

Demo: https://3v4l.org/RWcMu