[R] using tapply on a data frame in a function

[Peter Dalgaard]

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')
>
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>
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>   


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