Extract r.squared from multiple models with purrr::map()

Question

I have the following three linear models:

models <- mtcars %>% 
  split(.$cyl) %>% 
  map(~lm(mpg ~ wt, data = .))

Now I want to extract r.squared from all of the three models with purrr::map(). I've tried the following two ways but they both produce an error (i.e., "Error: Can't convert a summaryDefault/table object to function"):

models %>% 
  map(summary) %>% 
  map_dbl(~.$r.squared)

models %>% 
  map(summary) %>% 
  map_dbl("r.squared")

What's the issue and how can it be solved?

Answer 1

library(tidyverse)

models <- mtcars %>% 
  split(.$cyl) %>% 
  map(~lm(mpg ~ wt, data = .))

Manually doing it you can do:

summary(models[[1]])$r.squared

And then using map:

#and in map loop map_dfr
map_dfr(models, ~summary(.)$r.squared)
# # A tibble: 1 x 3
#     `4`   `6`   `8`
#   <dbl> <dbl> <dbl>
# 1 0.509 0.465 0.423

Or

 map_dfr(models, ~ glance(.x) %>%
                   dplyr::select(r.squared))

# A tibble: 3 x 1
#  r.squared
#      <dbl>
#1     0.509
#2     0.465
#3     0.423