[R] aggregation with two statistical functions - mean and variance

[Agrarimmobilien]

Hello, 

using the syntax 

aggregate(daten[,c(3,4)], list(A,B), mean)

I'm getting the following data.frame:


    A     B        C                    D       
1  35    1         6.16000          5
2  47    1        31.24333         20
3  54    1        26.81773         2
4   3     2        12.99000         7
5   4     2         6.49000          1

C and D are both means. But now I want to have: C is mean, D is variance. 

How can I do this by using/ changing the aggregation syntax?

Thanks! 

Macki