Lag/lead groups of observation with R

Question

I have a data frame like this one

id year var
1  2000 0
1  2000 0
1  2001 1
1  2001 0
1  2001 0
1  2002 1
1  2002 0
1  2003 1
2  2004 0
2  2004 1
2  2005 0
2  2006 0
2  2006 0
2  2007 1

I want to group my dataframe by id and year and create a "leaded" variable by group. In other words I want to obtain this output

id year var leadvar
1  2000 0   1
1  2000 0   1
1  2001 1   0
1  2001 1   0
1  2001 1   0
1  2002 0   1
1  2002 0   1
1  2003 1   NA
2  2004 0   0
2  2004 0   0
2  2005 0   0
2  2006 0   1
2  2006 0   1
2  2007 1   NA

where leadvar is just the value taken by the variable var for the same id in the subsequent year. Can anyone help me with this?

Many thanks.

Answer 1

One dplyr option could be:

df %>%
 group_by(id) %>%
 mutate(lead_var = lead(var)) %>%
 group_by(id, year) %>%
 mutate(lead_var = last(lead_var))

      id  year   var lead_var
   <int> <int> <int>    <int>
 1     1  2000     0        1
 2     1  2000     0        1
 3     1  2001     1        0
 4     1  2001     1        0
 5     1  2001     1        0
 6     1  2002     0        1
 7     1  2002     0        1
 8     1  2003     1       NA
 9     2  2004     0        0
10     2  2004     0        0
11     2  2005     0        0
12     2  2006     0        1
13     2  2006     0        1
14     2  2007     1       NA