[R] Data length mismatch.

[rkevinburton at charter.net]

I have two vectos (list) that represent a years of data.  Each "row" is represented by the day of year and the quantity that was sold for that day. I would like to form a new vector that is the difference between the two years of data. A sample of A (and similarly B) looks like:

> A[1:5,]
  DayOfYear    x
1         1 1429
2         2 3952
3         3 3049
4         4 2844
5         5 2219
> 

D <- A - B

This works just fine if A and B are both the same length. How is the best way to handle the situation where A and B are of different lengths? If the day of year exists in both vectors (lists) then I just want the coorespondng "row" in D to be the difference btween A and B values. If the "row" doesn't exist in either A or B then the difference should be treated as if the missing "row" was zero. Is this feasible?

Thank you.

Kevin