Create a panel data frame

Question

I would like to create a panel from a dataset that has one observation for every given time period such that every unit has a new observation for every time period. Using th

Answer 1

Using data.table:

require(data.table)
DT <- data.table(frame, key=c("id", "year"))
comb <- CJ(1:4, 2005:2008) # like 'expand.grid', but faster + sets key
ans <- DT[comb][is.na(y), y:=0L] # perform a join (DT[comb]), then set NAs to 0
#     id year y
#  1:  1 2005 1
#  2:  1 2006 0
#  3:  1 2007 0
#  4:  1 2008 0
#  5:  2 2005 0
#  6:  2 2006 0
#  7:  2 2007 0
#  8:  2 2008 0
#  9:  3 2005 0
# 10:  3 2006 0
# 11:  3 2007 0
# 12:  3 2008 0
# 13:  4 2005 0
# 14:  4 2006 0
# 15:  4 2007 1
# 16:  4 2008 0