How to assign IDs for consecutive rows in R split by a given kind of row? [duplicate]

Answer 1

data:

df <- data.frame(A = c(1:3,1,3,3,1,4))

code:

df$familiy_id <- cumsum(c(-1,diff(df$A)) < 0)

result:

#  A familiy_id
#1 1          1
#2 2          1
#3 3          1
#4 1          2
#5 3          2
#6 3          2
#7 1          3
#8 4          3

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please note:

This solution starts a new group when a number occurs that is smaller than the previous one.

When its 100% sure that a new group always begins with a 1 consistently, then ronak's solution is perfect.