[R] Odp: Getting mean in a dataframe

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 13.11.2007 23:29:25:

> Sorry to hijack this thread. I have a similar but slightly different 
> situation. Using the original poster's example, how to elegantly get 
> the mean of column V2 when column V1 is either A or C and F1 is 0?

I do not fully understand. You want to select subset of a data frame and 
then to compute column mean?

If yes just use ?subset or construct a logical vector according to your 
condition

lll <- (V1 == "A" | V1 == "B") & F1 == 0
mean(data[lll,"V2"])

Regards
Petr


> 
> Thanks,
> Gang
> 
> 
> On Nov 13, 2007, at 5:30 AM, Petr PIKAL wrote:
> > 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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> 
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