R help - Jun 2009 - Calculating "row standard deviations"

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?

Thanks!

Mark Na

Tena koe Mark

I think you might want

apply(datac, 1, mean) 

i.e., apply the function to the first dimension (rows) rather than the
second (columns).

HTH ...

Peter Alspach
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Mark Na
> Sent: Tuesday, 23 June 2009 10:20 a.m.
> To: r-help at r-project.org
> Subject: [R] Calculating "row standard deviations"
> 
> 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$Mean2<-apply(datac,2,mean)
> Error in dimnames(x) <- dn :
>   length of 'dimnames' [2] not equal to array extent
> 
> 
> Can anyone see what I'm doing wrong?
> 
> Thanks!
> 
> Mark Na
> 
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Mark Na wrote:
> Hi R-helpers,
> 
> I have been struggling with calculating row and column statistics,
> e.g. standard deviation.
> 
> I know that
>> datac$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             ?ster Farimagsgade 5, Entr.B
   c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
  (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907

On Jun 22, 2009, at 6:19 PM, 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
If you are trying to create a group means value for each element in an  
array or data.frame then the function to use is ave with its default  
function is mean. Other functions can be used but that is not  
necessary here. You could try:

datac$Mean2<-apply(datac,2,ave)

>
>
> Can anyone see what I'm doing wrong?
>
> Thanks!
>
> Mark Na
David Winsemius, MD
Heritage Laboratories
West Hartford, CT