PHP Using an If-else inside multidimensional associative array

My multidimensional associative array :

$search_cookies = array( 
    "type_catalog"  => $type_array,
    "size_catalog"  => $size_array,
    "color_catalog" => $color_array,
    );

I need to do that :

$search_cookies = array( 
    if(isset($type_array){
        "type_catalog"  => $type_array,
    }
    elseif(isset($size_array)){
        "size_catalog"  => $size_array,
    }
    elseif(isset($color_array)){
        "color_catalog"  => $color_array,
    }
    );

Here is the entire code if you think it must be some other way :

$first_array = array('t-1', 's-32', 't-2', 's-36');

function removeLetters($row){
    return preg_replace("/[^0-9,.]/", "", $row);
}

foreach($first_array as $row){
    $exp_key = explode('-', $row);
    if($exp_key[0] == 't'){
        $type_array[] = removeLetters($row);
    }
    if($exp_key[0] == 's'){
        $size_array[] = removeLetters($row);
    }
    if($exp_key[0] == 'c'){
        $color_array[] = removeLetters($row);
    }
}

$search_cookies = array( 
    "type_catalog"  => $type_array,
    "size_catalog"  => $size_array,
    "color_catalog" => $color_array,
    );