Subsetting a unbalanced panel dataset to have at least 2 consecutive observations in R

Question

I have an unbalanced panel dataset in R. The following will serve as an example:

dt <- data.frame(name= rep(c("A", "B", "C"), c(3,2,3)), 
                 year=c(2001:2003,2000,2002,2000:2001,2003))

> dt
  name year
1    A 2001
2    A 2002
3    A 2003
4    B 2000
5    B 2002
6    C 2000
7    C 2001
8    C 2003

Now, I need to have at least 2 consecutive year observations for each name. Hence, I would like to remove row 4, 5, and 8. How do I best do that in R?

EDIT: Thanks to the comment below, I can make a bit clearer. If I had an extra observation (row 9) with name=C and year=2004, I would want to keep both row 8 and 9 along with the others.

Answer 1

My (hackish) way to do it would be:

is.consecutive = duplicated(rbind(dt,transform(dt, year=year+1), 
                                     transform(dt, year=year-1)),
                            fromLast=TRUE)[1:nrow(dt)]

is.consecutive contains a vector of booleans of the observations to be retained. For your example, this vector would be: TRUE TRUE TRUE FALSE FALSE TRUE TRUE FALSE

Finally, you can easily use this vector to subset your data.frame, e.g. with:

dt[is.consecutive,]

Answer 2

Here's a more (far too...?) convoluted alternative, where you can set the minimum length of runs of consecutive observations.

dt <- dt[order(dt$name, dt$year), ]

rl <- 2

do.call(rbind,
        by(dt, dt$name, function(x){
          run <- c(0, cumsum(diff(x$year) > 1))
          x[ave(run, run, FUN = length) >= rl, ]
        })
)
#     name year
# A.1    A 2001
# A.2    A 2002
# A.3    A 2003
# C.6    C 2000
# C.7    C 2001

rl <- 3

do.call(rbind,
        by(dt, dt$name, function(x){
          run <- c(0, cumsum(diff(x$year) > 1))
          x[ave(run, run, FUN = length) >= rl, ]
        })
)
#     name year
# A.1    A 2001
# A.2    A 2002
# A.3    A 2003