How to merge first level keys with their second level values and remove all associative keys?

Question

I have array like this :

Array (
    [2018-03-12] => Array (
        [United States] => 4
        [Australia] => 15
        [United Kingdom] => 0
        [New Zealand] => 0
    )
    [2018-03-13] => Array (
        [United States] => 0
        [Australia] => 8
        [United Kingdom] => 2
        [New Zealand] => 0
    )
)

I want to make an array like this:

[
    ["2018-03-12", 4, 15, 0, 0],
    ["2018-03-13", 0, 8, 0, 2]
]

How can this be done?

Answer 1

Try:

$arr = [
    '2018-03-12' => [
        'United States' => 4,
         'Australia' => 15,
         'United Kingdom' => 0,
         'New Zealand' => 0,
    ],
    '2018-03-13' => [
         'United States' => 0,
         'Australia' => 8,
         'United Kingdom' => 2,
         'New Zealand' => 0,
    ]
];

return array_map(function ($item, $key) {
    return array_merge([$key], array_values($item));
},$arr, array_keys($arr));

Demo https://implode.io/K8yHG0