[R] How to create unique factor from two factors? + Boostrap Q
Prof Brian Ripley
ripley at stats.ox.ac.uk
Sun Nov 9 14:29:01 CET 2003
Factor3 <- factor(unclass(Factor1) + nlevels(Factor1)*(unclass(Factor2)-1))
will give you the unique combinations, not labelled as you do but then I
don't think you need that.
On Sun, 9 Nov 2003, Scott Norton wrote:
> This might be easy but I'm very new to R and this question doesn't seem to
> have any nice keywords that bring up relevant search results when I search
> the CRAN search engine. Therefore, I'll plead (as I have in the recent
> past) Newbie status.
>
>
>
> I have a data frame with two factors (Factor 1 and 2) which together specify
> another unique level. I want to create a third factor in the data frame
> that captures this uniqueness.
>
> For example, say I had dataframe, Df, with Factors, 1 and 2. I want to
> create Factor 3 and add it to my Df dataframe.
>
> i.e.
>
> Df dataframe: WANT TO
>
> Row# Factor1 Factor2 CREATE THIS: Factor 3 Data
>
> 1 1 1 1 23
>
> 2 1 2 2 43
>
> 3 1 2 2 19
>
> 4 1 2 2 11
>
> 5 1 4 3 3
>
> 6 1 4 3 13
>
> 7 3 1 4 52
>
> 8 3 1 4 12
>
> 9 3 1 4 9
>
> 10 3 3 5 21
>
> 11 3 3 5 43
>
>
> 12 4 1 6 32
>
> 13 4 1 6 18
>
> 14 4 2 7 52
>
> 15 4 2 7 21
>
>
>
>
> and of course, I'm trying to create Factor 3 without loops..
>
>
>
> My end goal here (which I add because maybe I don't need to create Factor 3
> (although I'm still curious)), is to bootstrap "sample" Factor 3. I want to
> repeatedly grab, say, 3 levels of Factor 3, and take the mean of those
> levels (e.g. say in my first bootstrap sample, I grab levels 2,4, and 7 from
> Factor 3, then I want to take the mean of rows, 2,3,4,7,8,9,14,15). Of
> course, each sample from Factor 3 for my bootstrap will most likely have a
> differing number of rows since my experiment is not balanced. I'm not sure
> if this is an issue yet when I try to implement the "boot" function in R (I
> haven't gotten to that point yet).
The boot package will easily do this for you.
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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