How to unnest a single column from a nested list without unnesting all

I have a data frame (tibble) with multiple nested columns nested in a single list, like this example

nested= mtcars%>%
  nest(extra = c("drat", "wt" ,  "qsec" ,"vs",   "am",   "gear" ,"carb"))

How do I unnest a single column from this list, without unnesting all and renesting the ones I still nested.

For example, with this data, can I just unnest gsec?

Solution

You can use map() to grab out that column and then unnest that.

nested %>% 
  mutate(qsec = map(extra, "qsec")) %>% 
  unnest_longer(qsec)

Notice though that this might create problems depending on what you do. This is because you'll now potentially have duplicates with the rest of the nested data. Might be safer to just unnest and nest again.

# A tibble: 32 x 6
     mpg   cyl  disp    hp extra             qsec
   <dbl> <dbl> <dbl> <dbl> <list>           <dbl>
 1  21       6  160    110 <tibble [2 x 7]>  16.5
 2  21       6  160    110 <tibble [2 x 7]>  17.0
 3  22.8     4  108     93 <tibble [1 x 7]>  18.6
 4  21.4     6  258    110 <tibble [1 x 7]>  19.4
 5  18.7     8  360    175 <tibble [1 x 7]>  17.0
 6  18.1     6  225    105 <tibble [1 x 7]>  20.2
 7  14.3     8  360    245 <tibble [1 x 7]>  15.8
 8  24.4     4  147.    62 <tibble [1 x 7]>  20  
 9  22.8     4  141.    95 <tibble [1 x 7]>  22.9
10  19.2     6  168.   123 <tibble [1 x 7]>  18.3