Summarise

The summarise verb is used to obtain aggregate values, generally over a grouped variable.

The following highlights some of the common operations using summarise. Generally, summarise is preceded by a group_by operation, that is, the summary is performed over grouped variables, as shown:

# In the example below: 
# 1) We sorted the DataFrame by State Name using arrange 
# 2) We applied a group-by using Region, i.e., all resulting values would be aggregated using Region 
# 3) We calcuated the values for total rows using n(), the unique states belonging to each region using n_distinct 
#   the max & mean literacy using max and mean respectively 
#  
 
tstate %>% arrange(Name) %>% group_by(Region) %>%  
  summarise(total_rows = n(), first_state = first(Name),  
unique_states = n_distinct(Name), max_literacy = max(100-Illiteracy), mean_literacy = mean(100-Illiteracy, na.rm=T)) 

The output is as follows: