Re: [R] Aggregate to find majority level of a factor

From: Marc Schwartz <marc_schwartz_at_comcast.net>
Date: Thu, 31 May 2007 15:32:46 -0500

On Thu, 2007-05-31 at 12:25 -0700, 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

Jonathan,

Try this:

> DF

     V1 V2
1 Plot1 big
2 Plot1 big
3 Plot1 small
4 Plot2 big
5 Plot2 small
6 Plot2 small
7 Plot3 small
8 Plot3 small
9 Plot3 small

> with(DF, aggregate(V2, list(V1), function(x) names(which.max(table(x)))))
  Group.1 x
1 Plot1 big
2 Plot2 small
3 Plot3 small

See ?which.max, ?names and ?table.

HTH, Marc Schwartz



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