Dear Mao,
Here is another way:

yourdata$traits2 <- with(yourdata, do.call(c, tapply(traits, group,
function(y){
                                                         ym <-
mean(y,na.rm=TRUE)
                                                         y[is.na(y)]<- ym
                                                         y
                                                       }
                                              )))

HTH,

Jorge


On Mon, Jun 8, 2009 at 9:56 PM, Mao Jianfeng <jianfeng....@gmail.com> wrote:

> Dear Ruser's
>
> I ask for helps on how to substitute missing values (NAs) by mean of the
> group it is belonging to.
>
> my dummy dataframe is:
>
> > df
>       group traits
> 1  BSPy01-10     NA
> 2  BSPy01-10    7.3
> 3  BSPy01-10    7.3
> 4  BSPy01-11    5.3
> 5  BSPy01-11    5.4
> 6  BSPy01-11    5.6
> 7  BSPy01-11     NA
> 8  BSPy01-11     NA
> 9  BSPy01-11    4.8
> 10 BSPy01-12    8.1
> 11 BSPy01-12    6.0
> 12 BSPy01-12    6.0
> 13 BSPy01-13    6.1
>
>
> I want to substitute each "NA" by the group mean of which the "NA" is
> belonging to. For example, substitute the first record of traits "NA" by
> the
> mean of "BSPy01-10".
>
> I have ever tried to solve this problem by using doBy package. But, I
> failed. I ask for the right solutions by using doBy package or not.
>
> The commands used and the output I got are as followed:
>
> library(doBy)
> df<-orderBy(~group,data=df)   # succeeded
> f1<-function(x){m<-mean(x, na.ram=TRUE); x[is.na(x)]<-m; x} # succeeded
> datatraits<-lapplyBy(traits~group,data=df, FUN=f1(traits)) # failed
> errors: mean(x, na.ram = TRUE), can not find 'traits'.
>
> Thanks in advance.
>
> Sincerely,
>
> Mao J-F
>
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>
> ______________________________________________
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>

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