如何在purrr:::map_df之后使用映射向量添加列

I'm using the mtcars dataset as an example to illustrate my question. I ran linear regression on each cylinder type and put all model result together using map_df. (Code and output below). What I want to do is adding another column named 'cylinder' (4,4,6,6,8,8). How can I do that in map_df? When I add argument .id='cylinder', I only got a column as 1,1,2,2,3,3. Thanks a lot in advance.I'm using the mtcars dataset as an example to i