r - Create counter with multiple variables -

this question has answer here:

• numbering rows within groups in data frame 2 answers

i have data looks below:

customerid tripdate 1           1/3/2013 1           1/4/2013 1           1/9/2013 2           2/1/2013 2           2/4/2013 3           1/2/2013 

i need create counter variable, below:

customerid tripdate   tripcounter 1           1/3/2013   1 1           1/4/2013   2  1           1/9/2013   3 2           2/1/2013   1 2           2/4/2013   2  3           1/2/2013   1  

tripcounter each customer.

use ave. assuming data.frame called "mydf":

mydf$counter <- with(mydf, ave(customerid, customerid, fun = seq_along)) mydf #   customerid tripdate counter # 1          1 1/3/2013       1 # 2          1 1/4/2013       2 # 3          1 1/9/2013       3 # 4          2 2/1/2013       1 # 5          2 2/4/2013       2 # 6          3 1/2/2013       1 

for it's worth, implemented version of approach in function included in "splitstackshape" package. function called getanid:

mydf <- data.frame(ida = c("a", "a", "a", "b", "b", "b", "b"),                    idb = c(1, 2, 1, 1, 2, 2, 2), values = 1:7) mydf # install.packages("splitstackshape") library(splitstackshape) # getanid(mydf, id.vars = c("ida", "idb")) getanid(mydf, id.vars = 1:2) #   ida idb values .id # 1     1      1   1 # 2     2      2   1 # 3     1      3   2 # 4   b   1      4   1 # 5   b   2      5   1 # 6   b   2      6   2 # 7   b   2      7   3 

as can see example above, i've written function in such way can specify 1 or more columns should treated id columns. checks see if of id.vars duplicated, , if are, generates new id variable you.