Get summary of the model using purrr::map within dplyr piping - r

Question

Using mtcars data, I am testing map() to build some lm() models:
library(tidyverse)
mtcars %>%
group_by(cyl) %>%
nest()%>%
mutate(fit = map(.x=data,~lm(mpg ~ ., data = .x)))
#> # A tibble: 3 x 3
#> cyl data fit
#> <dbl> <list> <list>
#> 1 6 <tibble [7 x 10]> <S3: lm>
#> 2 4 <tibble [11 x 10]> <S3: lm>
#> 3 8 <tibble [14 x 10]> <S3: lm>
The output shows that I have a new column, fit.
Now I wish to see the summary of each lm
When I try:
library(tidyverse)
mtcars %>%
group_by(cyl) %>%
nest()%>%
mutate(fit = map(.x=data,~lm(mpg ~ ., data = .x))) %>%
map(fit,summary)
#> Error in as_mapper(.f, ...): object 'fit' not found
It gives the error:
Error in as_mapper(.f, ...) : object 'fit' not found
If I wish to calculate R2 or aic then I can using the following code without any problem:
library(tidyverse)
library(modelr)
mtcars %>%
group_by(cyl) %>%
nest()%>%
mutate(fit = map(.x=data,~lm(mpg ~ ., data = .x))) %>%
mutate(r2 = map_dbl(fit, ~rsquare(., data = mtcars)),
aic = map_dbl(fit, ~AIC(.))) %>%
arrange(aic)
#> # A tibble: 3 x 5
#> cyl data fit r2 aic
#> <dbl> <list> <list> <dbl> <dbl>
#> 1 6 <tibble [7 x 10]> <S3: lm> -8.96 -Inf
#> 2 4 <tibble [11 x 10]> <S3: lm> -26.4 56.4
#> 3 8 <tibble [14 x 10]> <S3: lm> -1.000 67.3
Created on 2019-06-18 by the reprex package (v0.3.0)
What am I missing?

Answer 1

As IceCreamToucan's comment laid out, purrr::map does not look into the data which has been made within your piping.
If you use it with dplyr::mutate then it has access to fit which you have created in the previous piping.
Another option would be explicitly referring to fit which you can see below, as my second suggestion.
library(tidyverse)
mtcars %>%
group_by(cyl) %>%
nest()%>%
mutate(fit = map(.x=data,~lm(mpg ~ ., data = .x))) %>%
mutate(fit_sum = map(fit,summary))
#> # A tibble: 3 x 4
#> cyl data fit fit_sum
#> <dbl> <list> <list> <list>
#> 1 6 <tibble [7 x 10]> <lm> <smmry.lm>
#> 2 4 <tibble [11 x 10]> <lm> <smmry.lm>
#> 3 8 <tibble [14 x 10]> <lm> <smmry.lm>
mtcars %>%
group_by(cyl) %>%
nest()%>%
mutate(fit = map(.x=data,~lm(mpg ~ ., data = .x))) %>%
{map(.$fit, summary)} #or using pull: `pull(fit) %>% map(summary)`
#> [[1]]
#>
#> Call:
#> lm(formula = mpg ~ ., data = .x)
#>
#> Residuals:
#> ALL 7 residuals are 0: no residual degrees of freedom!
#>
#> Coefficients: (3 not defined because of singularities)
#> Estimate Std. Error t value Pr(>|t|)
#> (Intercept) 32.78649 NA NA NA
#> disp 0.07456 NA NA NA
#> hp -0.04252 NA NA NA
#> drat 1.52367 NA NA NA
#> wt 5.12418 NA NA NA
#> qsec -2.33333 NA NA NA
#> vs -1.75289 NA NA NA
#> am NA NA NA NA
#> gear NA NA NA NA
#> carb NA NA NA NA
#>
#> Residual standard error: NaN on 0 degrees of freedom
#> Multiple R-squared: 1, Adjusted R-squared: NaN
#> F-statistic: NaN on 6 and 0 DF, p-value: NA
####truncated the results for the sake of space####
Created on 2019-06-17 by the reprex package (v0.3.0)

Answer 2

From the latest release of dplyr, tidyverse seems to be encouraging using group_modify functions instead of using purrr + nested dataframes.
In that workflow, here is how you can get both model summaries and estimates in the same dataframe via broom package:
# setup
set.seed(123)
library(tidyverse)
options(tibble.width = Inf)
# joining dataframes with regression estimates and model summaries
dplyr::full_join(
# to get a tidy dataframe of regression estimates
x = mtcars %>%
group_by(cyl) %>%
group_modify(.f = ~ broom::tidy(lm(mpg ~ ., data = .x), conf.int = TRUE)),
# to get a tidy dataframe of model summaries
y = mtcars %>%
group_by(cyl) %>%
group_modify(.f = ~ broom::glance(lm(mpg ~ ., data = .x))),
by = "cyl"
) %>%
dplyr::ungroup(x = .)
#> Warning in qt(a, object$df.residual): NaNs produced
#> # A tibble: 25 x 20
#> cyl term estimate std.error statistic.x p.value.x conf.low
#> <dbl> <chr> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1 4 (Intercept) 60.9 180. 0.338 0.793 -2229.
#> 2 4 disp -0.345 0.469 -0.735 0.596 -6.31
#> 3 4 hp -0.0332 0.364 -0.0915 0.942 -4.65
#> 4 4 drat -4.19 46.4 -0.0903 0.943 -594.
#> 5 4 wt 4.48 29.7 0.151 0.905 -373.
#> 6 4 qsec -0.106 7.82 -0.0136 0.991 -99.4
#> 7 4 vs -3.64 34.0 -0.107 0.932 -435.
#> 8 4 am -6.33 45.2 -0.140 0.912 -581.
#> 9 4 gear 4.07 29.1 0.140 0.912 -366.
#> 10 4 carb 3.22 28.2 0.114 0.928 -355.
#> conf.high r.squared adj.r.squared sigma statistic.y p.value.y df
#> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1 2351. 0.928 0.276 3.84 1.42 0.576 9
#> 2 5.62 0.928 0.276 3.84 1.42 0.576 9
#> 3 4.59 0.928 0.276 3.84 1.42 0.576 9
#> 4 586. 0.928 0.276 3.84 1.42 0.576 9
#> 5 382. 0.928 0.276 3.84 1.42 0.576 9
#> 6 99.2 0.928 0.276 3.84 1.42 0.576 9
#> 7 428. 0.928 0.276 3.84 1.42 0.576 9
#> 8 568. 0.928 0.276 3.84 1.42 0.576 9
#> 9 374. 0.928 0.276 3.84 1.42 0.576 9
#> 10 362. 0.928 0.276 3.84 1.42 0.576 9
#> logLik AIC BIC deviance df.residual nobs
#> <dbl> <dbl> <dbl> <dbl> <int> <int>
#> 1 -17.2 56.4 60.8 14.7 1 11
#> 2 -17.2 56.4 60.8 14.7 1 11
#> 3 -17.2 56.4 60.8 14.7 1 11
#> 4 -17.2 56.4 60.8 14.7 1 11
#> 5 -17.2 56.4 60.8 14.7 1 11
#> 6 -17.2 56.4 60.8 14.7 1 11
#> 7 -17.2 56.4 60.8 14.7 1 11
#> 8 -17.2 56.4 60.8 14.7 1 11
#> 9 -17.2 56.4 60.8 14.7 1 11
#> 10 -17.2 56.4 60.8 14.7 1 11
#> # ... with 15 more rows
Created on 2019-06-17 by the reprex package (v0.3.0)