Extracting elements from a tibble

In R, I frequently find myself trying to extract elements out of a tibble. This is especially the case when I’m trying to take out a summary statistic.

For example, the code below produces the mean of the hwy column in the vehicles dataset:

library(dplyr)
library(fueleconomy)
data(vehicles)
mean_hwy <- vehicles %>% summarize(mean_hwy = mean(hwy))
mean_hwy
# # A tibble: 1 x 1
#   mean_hwy
#      <dbl>
# 1     23.6

Let’s say I want to extract 23.6 from the tibble above. My instinct is to subset the tibble just like a matrix, but it returns another tibble!

mean_hwy[1,1]
# # A tibble: 1 x 1
#   mean_hwy
#      <dbl>
# 1     23.6

The way to get around this is to use $ or [[, as you would when subsetting a list:

mean_hwy[[1]]
# [1] 23.55128
mean_hwy$mean_hwy
# [1] 23.55128

For more details, see R for Data Science‘s chapter on Tibbles.

Update (2019-08-29): As Paul mentions in the comments, the dplyr package has a pull() function which allows you to extract a column as a vector:

mean_hwy %>% pull(mean_hwy)
# [1] 23.55128