[R] Odp: tapply, mean and subset

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 13.11.2007 10:59:09:

> 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

I would use ave for computing mean for combination of V1 and F1 and then I 
put all values of F1_mean for which F1 is 1 to 0

test$F1_mean <- ave(test$V2, test$V1, factor(test$F1), FUN = mean)
test$F1_mean[test$F1==1] <- 0

Regards
Petr

> 
> Thank you for any help!
> 
> Patrick Hausmann
> 
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