R help - Sep 2008 - using tapply on a data frame in a function

Hello,

I'm trying to use tapply to find group means in a function.  It works
outside of a function, but I get the error message from the following code:
"Error in tapply(index, cluster, mean) : arguments must have same
length."
Any suggestions?  Thanks.

eric

d <- data.frame(cbind(cluster=1:2, value1=1:10, value2=11:20))
d

FindClusterTraits <- function(framename, index){
    MeanCluster <- with(framename, tapply(index, cluster, mean))
    return(MeanCluster)
}

d2 <- FindClusterTraits(d, 'value1')

	[[alternative HTML version deleted]]

eric lee wrote:
> Hello,
>
> I'm trying to use tapply to find group means in a function.  It works
> outside of a function, but I get the error message from the following code:
> "Error in tapply(index, cluster, mean) : arguments must have same
length."
> Any suggestions?  Thanks.
>   
This is neither caused by tapply, data frames, nor functions....

You are trying to use a character string ('value1') as if it were a 
variable name. It wouldn't work either to say tapply('value1',
cluster,
mean) would it?

You might be looking for tapply(framename[[index]],....), or 
with(framename, tapply(get(index), ....)),
or maybe some concoction involving substitute().
> eric
>
> d <- data.frame(cbind(cluster=1:2, value1=1:10, value2=11:20))
> d
>
> FindClusterTraits <- function(framename, index){
>     MeanCluster <- with(framename, tapply(index, cluster, mean))
>     return(MeanCluster)
> }
>
> d2 <- FindClusterTraits(d, 'value1')
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide
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>   

-- 
   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

eric lee <ericlee100 <at> gmail.com> writes:
> 
> Hello,
> 
> I'm trying to use tapply to find group means in a function.  It works
> outside of a function, but I get the error message from the following code:
> "Error in tapply(index, cluster, mean) : arguments must have same
length."
> Any suggestions?  Thanks.
> 
> eric
> 
> d <- data.frame(cbind(cluster=1:2, value1=1:10, value2=11:20))
> d
> 
> FindClusterTraits <- function(framename, index){
>     MeanCluster <- with(framename, tapply(index, cluster, mean))
>     return(MeanCluster)
> }
> 
> d2 <- FindClusterTraits(d, 'value1')
> 
Thanks for the self-running example! Not really a function problem, though.

d <- data.frame(cbind(cluster=1:2, value1=1:10, value2=11:20))
d

FindClusterTraits <- function(framename, index){
  tapply(framename[[index]], framename[["cluster"]], mean)
}

FindClusterTraits(d, 'value1')

Note that the return(MeanCluster) is not required in R.

Dieter