using dplyr's do() with summary()

Question

I would like to be able to use dplyr's split-apply-combine strategy to the apply the summary() command.

Take a simple data frame:

df <- data.frame(class = c('A', 'A', 'B', 'B'),
                 value = c(100, 120, 800, 880))

Ideally we would do something like this:

df %>%
  group_by(class) %>%
  do(summary(.$value))

Unfortunately this does not work. Any ideas?

Answer 1

You can use the SE version of data_frame, that is, data_frame_ and perform:

df %>%
  group_by(class) %>%
  do(data_frame_(summary(.$value)))

Alternatively, you can use as.list() wrapped by data.frame() with the argument check.names = FALSE:

df %>%
  group_by(class) %>%
  do(data.frame(as.list(summary(.$value)), check.names = FALSE))

Both versions produce:

# Source: local data frame [2 x 7]
# Groups: class [2]
# 
#    class  Min. 1st Qu. Median  Mean 3rd Qu.  Max.
#   (fctr) (dbl)   (dbl)  (dbl) (dbl)   (dbl) (dbl)
# 1      A   100     105    110   110     115   120
# 2      B   800     820    840   840     860   880