[R] Aggregate to find majority level of a factor

[Mike Lawrence]

This should do the trick. Also labels ties with NA.

a=as.data.frame(cbind(c(1,1,1,2,2,2,3,3,3,4,4),c 
('big','big','small','big','small','small','small','small','small','big' 
,'small')))
a$V2=factor(a$V2)

maj=function(x){
	y=table(x)
	z=which.max(y)
	if(sum(y==max(y))==1){
		return(names(y)[z])
	}else{
		return(NA)
	}
}

aggregate(a$V2,list(a$V1),maj)


On 31-May-07, at 4:25 PM, Thompson, Jonathan wrote:

> I want to use the aggregate function to summarize data by a factor (my
> field plots), but I want the summary to be the majority level of  
> another
> factor.
>
>
> For example, given the dataframe:
>
> Plot1     big
> Plot1     big
> Plot1     small
> Plot2     big
> Plot2     small
> Plot2     small
> Plot3     small
> Plot3     small
> Plot3     small
>
>
> My desired result would be:
> Plot1 big
> Plot2 small
> Plot3 small
>
>
> I can't seem to find a scalar function that will give me the majority
> level.
>
> Thanks in advance,
>
> Jonathan Thompson
>
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> and provide commented, minimal, self-contained, reproducible code.

--
Mike Lawrence
Graduate Student, Department of Psychology, Dalhousie University

Website: http://myweb.dal.ca/mc973993
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