using tapply on a data frame in a function

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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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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