def get_all_tokens_in_dataset(X_train_tokenized, X_test_tokenized):
    """returns a list including all unique tokens in train and test set
    
    Arguments:
        X_train_tokenized {DataFrame} -- train set
        X_test_tokenized {DataFrame} -- test set
    
    Returns:
        list -- list of unique tokens
    """

    X_train_sublists = X_train_tokenized.values.flatten()
    X_train_tokens = set([item for sublist in X_train_sublists for item in sublist])    
    X_test_sublists = X_test_tokenized.values.flatten()
    X_test_tokens = set([item for sublist in X_test_sublists for item in sublist])
    return list(X_train_tokens | X_test_tokens)