7.1 count()

What it does: Collapses the rows and counts the number of observations per group of values.

Count the number of values for each cut:

diamonds %>% count(cut) 

# is the same as

diamonds %>% group_by(cut) %>% count()

# is the same as

diamonds %>% 
  group_by(cut) %>% 
  summarize(n = n())

Count the number of values for each cut and color:

diamonds %>% count(cut, clarity)

# is the same as
diamonds %>% group_by(cut, clarity) %>% count()
diamonds %>% group_by(cut, clarity) %>% summarize(n = n())