[SOLVED] Generating a lagged time series cross sectional variable in R

Generating a lagged time series cross sectional variable in R

I am a new R user. I have a time series cross-sectional dataset and, although I have found ways to lag time series data in R, I have not found a way to create lagged time-series cross-sectional variables so that I can use them in my analysis.

Solution

Here's how you could use the lag() function with zoo (and panel series data):

> library(plm)
> library(zoo)
> data("Produc")
> dnow <- pdata.frame(Produc)
> x.Date <- as.Date(paste(rownames(t(as.matrix(dnow$pcap))), "-01-01", sep=""))
> x <- zoo(t(as.matrix(dnow$pcap)), x.Date)
> x[1:3,1:3]
            ALABAMA  ARIZONA ARKANSAS
1970-01-01 15032.67 10148.42  7613.26
1971-01-01 15501.94 10560.54  7982.03
1972-01-01 15972.41 10977.53  8309.01

Lag forward by 1:

> lag(x[1:3,1:3],1)
            ALABAMA  ARIZONA ARKANSAS
1970-01-01 15501.94 10560.54  7982.03
1971-01-01 15972.41 10977.53  8309.01

Lag backward by 1:

> lag(x[1:3,1:3],k=-1)
            ALABAMA  ARIZONA ARKANSAS
1971-01-01 15032.67 10148.42  7613.26
1972-01-01 15501.94 10560.54  7982.03

As Dirk mentioned, be careful with the meaning of lag in the different time series packages. Notice how xts treats this differently:

> lag(as.xts(x[1:3,1:3]),k=1)
            ALABAMA  ARIZONA ARKANSAS
1970-01-01       NA       NA       NA
1971-01-01 15032.67 10148.42  7613.26
1972-01-01 15501.94 10560.54  7982.03