### R +1 Lag

In the last post I gave an example of how to use R to lag a variable in a time-series cross-sectional data set by one time unit. In other words, the value of the lagged variable at time \( t \) the lag would be the value of the unlagged variable at \( t-1 \).

Using the same example variables (`Country`

, `Year`

, `Variable`

) here is how you would lag the variable (`VariableLag1`

) back a year. So, in time t the value of `VariableLag`

would be the value of `Variable`

in \( t+1 \)).

Here is the code:

```
library(plyr)
Data <- ddply(Data, .(country), transform, VariableLag1 =
c(Variable[2:(length(Variable))], NA)
```