how to decide the longest continuous sequence in a long sequence in r

Question

I have a sequence as the toy example. how can I decide the longest continuous sub-sequence? for now, i can find where the breaking points are, how can I get the values?

DT <- data.table(X = c(3:7, 16:18, 22:29, 31:36))
DT[,Y:=(shift(.SD,type = "lag", fill = -1))][,Y:= Y-X]
with(DT, which(Y !=-1)) 

what I hope to find is the value of the subquence, in this case, shall be c(22, 23, 24, 25, 26, 27, 28, 29)

Answer 1

Not sure what is your expected output but here we add length of each sequence in the data.table

library(data.table)
DT[, length := .N, by = cumsum(c(1, diff(X) != 1))]

DT
#     X length
# 1:  3      5
# 2:  4      5
# 3:  5      5
# 4:  6      5
# 5:  7      5
# 6: 16      3
# 7: 17      3
# 8: 18      3
# 9: 22      8
#10: 23      8
#11: 24      8
#12: 25      8
#13: 26      8
#14: 27      8
#15: 28      8
#16: 29      8
#17: 31      6
#18: 32      6
#19: 33      6
#20: 34      6
#21: 35      6
#22: 36      6
#     X length

and then if you want to extract only max values, we can do

DT[length == max(length), ]

#    X length
#1: 22      8
#2: 23      8
#3: 24      8
#4: 25      8
#5: 26      8
#6: 27      8
#7: 28      8
#8: 29      8