[R] add one variable to a data frame

[Ding, Yuan Chun]

Hi All,

I have a data frame dat1:
dat1 <-data.frame(N=seq(1, 12,1), B=c("29_log","29_log", "29_log", "27_cat", "27_cat",
                                                                       "1_log", "1_log", "1_log", "1_log", "1_log",
                                                                        "3_cat", "3_cat"))

Then I need to add one column or variable to reflect uniqueness of B variable in sequential order as below.
dat1$C <-c(1,1,1,2,2,3,3,3,3,3,4,4)

I only show 12 rows, my real data frame has over 1000 rows, I can not manually to add column C.

It should be easy, but I can not figure out. Can you help me?

Thanks,

Ding


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