Call to a member function all() on string Laravel 5

i do sql

        $array_symbols_id = DB::table('symbol')
        ->whereIn('symbol_name', $array_symbols)
        ->pluck('symbol_id')
        ->all();
        print_r($array_symbols_id);

and throw exception

FatalErrorException in CompgenGetter.php line 54:
Call to a member function all() on string

in my array_symbols Array ( [0] => A [1] => S [2] => D [3] => F [4] => S [5] => A )

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