Extract residuals from models fit in purrr - r

Question

I grouped my data and fit a model to each group and I would like to have the residuals for each group. I can see the residuals for each model with RStudio's viewer, but I cannot figure out how to extract them. Extracting one set of residuals can be done like diamond_mods[[3]][[1]][["residuals"]], but how do I use purrr to extract the set from every group (along with broom to end up with a nice tibble)?
Below is how far I've gotten:
library(tidyverse)
library(purrr)
library(broom)
fit_mod <- function(df) {
lm(price ~ poly(carat, 2, raw = TRUE), data = df)
}
diamond_mods <- diamonds %>%
group_by(cut) %>%
nest() %>%
mutate(
model = map(data, fit_mod),
tidied = map(model, tidy)
#resid = map_dbl(model, "residuals") #this was my best try, it doesn't work
) %>%
unnest(tidied)

Answer 1

You were close - but you should use map() instead of map_dbl() as you need to return a list not a vector.
diamond_mods <- diamonds %>%
group_by(cut) %>%
nest() %>%
mutate(
model = map(data, fit_mod),
tidied = map(model, tidy),
resid = map(model, residuals)
)

Answer 2

With the devel version of dplyr, we can do this in condense after grouping by 'cut'
library(dplyr)
library(ggplot2)
library(broom)
diamonds %>%
group_by(cut) %>%
condense(model = fit_mod(cur_data()),
tidied = tidy(model),
resid = model[["residuals"]])
# A tibble: 5 x 4
# Rowwise: cut
# cut model tidied resid
# <ord> <list> <list> <list>
#1 Fair <lm> <tibble [3 × 5]> <dbl [1,610]>
#2 Good <lm> <tibble [3 × 5]> <dbl [4,906]>
#3 Very Good <lm> <tibble [3 × 5]> <dbl [12,082]>
#4 Premium <lm> <tibble [3 × 5]> <dbl [13,791]>
#5 Ideal <lm> <tibble [3 × 5]> <dbl [21,551]>