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<?php $array = [ '2018-03-12' => [ 'United States' => 4, 'Australia' => 15, 'United Kingdom' => 0, 'New Zealand' => 0, ], '2018-03-13' => [ 'United States' => 0, 'Australia' => 8, 'United Kingdom' => 2, 'New Zealand' => 0, ] ]; var_export( array_map( fn($k) => array_merge([$k], array_values($array[$k])), array_keys($array) ) );

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