[R] tapply, mean and subset

[c18g at uni-bremen.de]

Dear list,

I have this dataframe

   V1 V2 F1
1  A  2  0
2  A  3  0
3  A  4  1
4  B  3  0
5  B  2  1
6  C  6  0
7  C  2  0
8  C  6  0

and would like to calculate a new column
with mean-values, following this rule

1. If F1 = 0 calculate the mean from V2
for each factor in V1.

2. If F1 = 1, then F1_mean = 0

So, the new DF should look like this

   V1 V2 F1 F1_mean
1  A  2  0     2.5
2  A  3  0     2.5
3  A  4  1     0.0
4  B  3  0     3.0
5  B  2  1     0.0
6  C  6  0     7.0
7  C  2  0     7.0
8  C  6  0     7.0

Thank you for any help!

Patrick Hausmann