rename a column in a list of dataframes in using purrr::walk

Question

I need to rename the second columns for all the dataframes in a list. I'm trying to use purrr::walk.

Here is the code:

cyl.name<- c('4-cyl', '6-cyl', '8-cyl')
cyl<- c(4,6,8)    
car <- map(cyl, ~mtcars %>% filter(cyl==.x) %>%
                     group_by(gear) %>% 
                     summarise(mean=mean(hp)) )
walk (seq_along(cyl.name), function (x) names(car[[x]])[2]<- cyl.name[x])

When I check the columns names, all the mean column are still named 'mean'. What did I do wrong?

Answer 1

If you have the list of the column names like this, you could use map2 to simultaneously loop through the filter variable and the naming variable. This would allow you to name the columns as you go rather than renaming after making the list.

This does involve using some tidyeval operations from rlang for programming with dplyr .

map2(cyl, cyl.name, ~mtcars %>% 
         filter(cyl==.x) %>%
         group_by(gear) %>%
         summarise( !!.y := mean(hp)) )

[[1]]
# A tibble: 3 x 2
   gear `4-cyl`
  <dbl>   <dbl>
1     3      97
2     4      76
3     5     102

[[2]]
# A tibble: 3 x 2
   gear `6-cyl`
  <dbl>   <dbl>
1     3   107.5
2     4   116.5
3     5   175.0

[[3]]
# A tibble: 2 x 2
   gear  `8-cyl`
  <dbl>    <dbl>
1     3 194.1667
2     5 299.5000