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

An idea with data.table:

require(data.table)

dt <- fread("ID  State
1   A
            2   A
            3   B
            4   B
            5   B
            6   A
            7   A
            8   A
            9   C
            10  C")

dt[,rle := rleid(State)]
dt2<-dt[,list(min=min(ID),max=max(ID)),by=c("rle","State")]

which gives:

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

The idea is to identify sequences with rleid and then get the min and max of IDby the tuple rle and State.

you can remove the rle column with

dt2[,rle:=NULL]

Chained:

 dt2<-dt[,list(min=min(ID),max=max(ID)),by=c("rle","State")][,rle:=NULL]

---

You can shorten the above code even more by using rleid inside by directly:

dt2 <- dt[, .(min=min(ID),max=max(ID)), by=.(State, rleid(State))][, rleid:=NULL]