How to lag row number in R

Question

I have three columns and in fourth column i want a lag of third column. How to do this in R

For example

uid       timestamp    operation
 1         24-04-12    logged-in
 2         25-06-13    view content
 1         31-05-10    delete

But i want to use lag function as we do in SAS and want output as below

uid        timestamp    operation     lag
 1         24-04-12     logged-in      
 2         25-06-13     view content  logged-in
 3         31-05-10     delete        view content

I have lag function using zoo package ,but it is not happening , how to do this in R?? Any guidance will be much appreciated.

Answer 1

When using functions specific to the zoo package (eg ?lag.zoo ), you need to make sure the data you are operating on is a zoo object:

operation <- c("logged-in","view current", "delete")
lag(zoo(operation),-1,na.pad=TRUE)
#         1            2            3 
#      <NA>    logged-in view current 

lag(zoo(operation),1,na.pad=TRUE)
#           1            2            3 
#view current       delete         <NA> 

Otherwise, using base R, head (and tail ) can get you there:

# match the 1 and -1 to how big you want your lag:
c(rep(NA,1),head(operation,-1))
#[1] NA             "logged-in"    "view current"

c(tail(operation,-1),rep(NA,1))
#[1] "view current" "delete"       NA