[R] tapply, mean and subset

[Moshe Olshansky]

One possibility is:

a<-"   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
+ "

b<-read.table(textConnection(a),header=TRUE)
f<-rep(0,dim(b)[1])
f[b$F1==0] <- ave(b$V2[b$F1==0],b$V1[b$F1==0])
cbind(b,f)
  V1 V2 F1        f
1  A  2  0 2.500000
2  A  3  0 2.500000
3  A  4  1 0.000000
4  B  3  0 3.000000
5  B  2  1 0.000000
6  C  6  0 4.666667
7  C  2  0 4.666667
8  C  6  0 4.666667

--- c18g at uni-bremen.de wrote:

> 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
> 
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