df %>% group_by(category) %>% summarise(number = n())# dplyr package does this with count/tally commands, or the n() function: # First, some data: df <- data.frame(x = rep(1:6, rep(c(1, 2, 3), 2)), year = 1993:2004, month = c(1, 1:11)) # Now the count: library(dplyr) count(df, year, month) # piping df %>% count(year, month) # We can also use a slightly longer version with piping and the n() function: df %>% group_by(year, month) %>% summarise(number = n()) dplyr package does this with count/tally commands, or the n() function: # First, some data: df <- data.frame(x = rep(1:6, rep(c(1, 2, 3), 2)), year = 1993:2004, month = c(1, 1:11)) # Now the count: library(dplyr) count(df, year, month) # piping df %>% count(year, month) # We can also use a slightly longer version with piping and the n() function: df %>% group_by(year, month) %>% summarise(number = n()) # or the tally function: df %>% group_by(year, month) %>% tally()