R help - Jun 2013 - Calculate geometric mean with tapply

Hi,

I am trying to calculate the geometric mean with tapply. This is the
formula I am using:

exp(tapply(log(data$value), data$group, mean))


However, it returns the arithmetic mean. Any ideas?


Thanks


-- 
Shane

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Hello,

You can write a function gmean and tapply it to your data.


gmean <- function(x, na.rm = FALSE){
	if(na.rm) x <- x[!is.na(x)]
	n <- length(x)
	prod(x)^(1/n)
}

tapply(data$value, data$group, gmean)


Hope this helps,

Rui Barradas

Em 25-06-2013 11:58, Shane Carey escreveu:
> Hi,
>
> I am trying to calculate the geometric mean with tapply. This is the
> formula I am using:
>
> exp(tapply(log(data$value), data$group, mean))
>
>
> However, it returns the arithmetic mean. Any ideas?
>
>
> Thanks
>
>