Select first and last row from grouped data

Question

Question

Using dplyr, how do I select the top and bottom observations/rows of grouped data in one statement?

Data & Example

Given a data frame:

df <- data.frame(id=c(1,1,1,2,2,2,3,3,3),                   stopId=c("a","b","c","a","b","c","a","b","c"),                   stopSequence=c(1,2,3,3,1,4,3,1,2)) 

I can get the top and bottom observations from each group using slice, but using two separate statements:

firstStop <- df %>%   group_by(id) %>%   arrange(stopSequence) %>%   slice(1) %>%   ungroup  lastStop <- df %>%   group_by(id) %>%   arrange(stopSequence) %>%   slice(n()) %>%   ungroup 

Can I combine these two statements into one that selects both top and bottom observations?

Answer 1

There is probably a faster way:

df %>%   group_by(id) %>%   arrange(stopSequence) %>%   filter(row_number()==1 | row_number()==n())