Add column to 2d array mapped from a flat associative lookup array

I have an associative array of counts with brand_slug keys and a 2d array to which I would like to append related count data.

$countArray = [
    "abu-garcia" => 1,
    "daiwa" => 4,
    "shimano" => 4
];

$dataArray = [
    [
        "brand_id" => 36,
        "brand_name" => "Abu Garcia",
        "brand_slug" => "abu-garcia"
    ],
    [
        "brand_id" => 41,
        "brand_name" => "Daiwa",
        "brand_slug" => "daiwa"
    ],
    [
        "brand_id" => 41,
        "brand_name" => "Daiwa",
        "brand_slug" => "daiwa"
    ],
    [
        "brand_id" => 39,
        "brand_name" => "Shimano",
        "brand_slug" => "shimano"
    ],
    [
        "brand_id" => 39,
        "brand_name" => "Shimano",
        "brand_slug" => "shimano"
    ],
];

I want to create a new array which should look like this:

[
    [
        "brand_id" => 36,
        "brand_name" => "Abu Garcia",
        "brand_slug" => "abu-garcia",
        "count" => 1
    ],
    [
        "brand_id" => 41,
        "brand_name" => "Daiwa",
        "brand_slug" => "daiwa",
        "count" => 4,
    ],
    [
        "brand_id" => 41,
        "brand_name" => "Daiwa",
        "brand_slug" => "daiwa",
        "count" => 4
    ],
    [
        "brand_id" => 39,
        "brand_name" => "Shimano",
        "brand_slug" => "shimano",
        "count" => 4
    ],
    [
        "brand_id" => 39,
        "brand_name" => "Shimano",
        "brand_slug" => "shimano",
        "count" => 4
    ],
];

I think I understand what you're trying to do...

If these are examples of your arrays:

$CountArray = array("abu-garcia"=>1,
                "daiwa"=>4,
                "shimano"=>4);
$DataArray = array(
            array("brand_id"=>36, "brand_name"=>"Abu Garcia", "brand_slug"=>"abu-garcia"),
            array("brand_id"=>41, "brand_name"=>"Daiwa", "brand_slug"=>"daiwa"),
            array("brand_id"=>39, "brand_name"=>"Shimano", "brand_slug"=>"shimano")
);

Then loop through your second array to build a new array, and adding the count key from the first array like this:

$i = 0;
foreach($DataArray as $ItemArray){
    foreach($ItemArray as $Key=>$Value){
        $NewArray[$i][$Key] = $Value;
        $NewArray[$i]['count'] = 0;
        if(isset($CountArray[$ItemArray['brand_slug']])){
            $NewArray[$i]['count'] = $CountArray[$ItemArray['brand_slug']];         
        }
    }
    ksort($NewArray[$i]);
    $i++;
}
print_r($NewArray);