How to compute growth rate (1- and 3-year horizon) from panel data in R

I've a panel dataset of several banks, each from 1997 to 2015, with annual observations s.t.:

CODE      COUNTRY      YEAR      LOANS_NET      ...other variables
671405      AT         1997       39028938
671405      AT         1998       41033237
671405      AT         1999       35735062
...
...
671405      AT         2015      130701872
...
30885R      DE         2004      200024673
...
...

Using R, I need to compute additional two columns:

1) LOANS_NET growth rate at 1-year horizon

2) LOANS_NET growth rate at 3-years horizon, which must be annualized, once calculated.

E.g.:

Loan Growth 3-year = [Bank's(i) LOANS_NET Year(t) / Bank's(i) LOANS_NET Year(t-3)] -1

nb: data contains lots of missing values, code must consider that issue! :)

Solution

@Dan Do you use any packages? I recommend you using zoo and data.table packages and transform dates in the following way:

DT[, YearNumeric := as.numeric(YEAR)]
DT[, PreviousYearLoanNet := .SD[match(YearNumeric - 1, .SD$YearNumeric), LOANS_NET], by=CODE]

Here, you create a column with previous (-1 year) loan values. Then you create a new column with growth:

DT[,Growth1Y:= (YEARLOANNET- PreviousYearLoanNet)/PreviousYearLoanNet]

And then you do whatever you want:) Cheers!