Grouping of R dataframe by connected values

Question

I didn\'t find a solution for this common grouping problem in R:

This is my original dataset

ID  State
1   A
2   A
3   B
4   B
5   B
6   A
7   A
8            


        

Answer 1

You could try:

library(dplyr)
df %>%
  mutate(rleid = cumsum(State != lag(State, default = ""))) %>%
  group_by(rleid) %>%
  summarise(State = first(State), min = min(ID), max = max(ID)) %>%
  select(-rleid)

---

Or as per mentioned by @alistaire in the comments, you can actually mutate within group_by() with the same syntax, combining the first two steps. Stealing data.table::rleid() and using summarise_all() to simplify:

df %>% 
  group_by(State, rleid = data.table::rleid(State)) %>% 
  summarise_all(funs(min, max)) %>% 
  select(-rleid)

Which gives:

## A tibble: 4 × 3
#   State   min   max
#    
#1      A     1     2
#2      B     3     5
#3      A     6     8
#4      C     9    10