[R] Calculating "row standard deviations"

[Peter Dalgaard]

Mark Na wrote:
> Hi R-helpers,
> 
> I have been struggling with calculating row and column statistics,
> e.g. standard deviation.
> 
> I know that
>> datac$Mean<-rowMeans(datac,na.rm=TRUE)
> will give me row means.
> 
> I have tried to replicate those row means with the apply function:
>> datac$Mean2<-apply(datac,2,mean)
> 
> so that I can replace the function argument with "sd" (instead of
> mean) to get standard deviations.
> 
> But, I'm running into this error:
> 
>> dim(datac)
> [1]  17 271
>> datac$Mean2<-apply(datac,2,mean)
> Error in dimnames(x) <- dn :
>   length of 'dimnames' [2] not equal to array extent
> 
> 
> Can anyone see what I'm doing wrong?

Not really, but you need apply(datac,1,mean) for row means:

 > apply(airquality,2,mean)
     Ozone   Solar.R      Wind      Temp     Month       Day
        NA        NA  9.957516 77.882353  6.993464 15.803922

which are obviously column means.
However, I see a different error if I try to assign that back

 > airquality$m <- apply(airquality,2,mean)
Error in `$<-.data.frame`(`*tmp*`, "m", value = c(NA, NA, 
9.95751633986928,  :
   replacement has 6 rows, data has 153

Can't get much closer without a REPRODUCIBLE example.

-- 
    O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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