[R] tapply bug? - levels of a factor in a data frame after tapply are intermixed

[jim holtman]

Think of the levels as a table you are going to index into.  The
factors that you see (2, 1, 3) are the indices into the levels so you
get 9, 3, 15 as the result.

What were you expecting?  It is working as it is supposed to.

On Fri, Feb 13, 2009 at 12:09 PM, Dimitri Liakhovitski <ld7631 at gmail.com> wrote:
> Hello! I have encountered a really weird problem. Maybe you've
> encountered it before?
> I have a large data frame "importances". It has one factor ($A) with 3
> levels: 3, 9, and 15. $B is a regular numeric variable.
> Below I am picking a really small sub-frame (just 3 rows) based on
> "indices". "indices" were chosen so that all 3 levels of A are
> present:
>
> indices=c(14329,14209,14353)
> test=data.frame(yy=importances[["B']][indices],xx=importances[["A"]][indices])
> Here is what the new data frame "test" looks like:
>
>            yy        xx
> 1 -0.009984006  9
> 2 -2.339904131  3
> 3 -0.008427385 15
>
> Here is the structure of "test":
>>str(test)
> 'data.frame':   3 obs. of  2 variables:
>  $ yy: num  -0.00998 -2.3399 -0.00843
>  $ xx: Factor w/ 3 levels "3","9","15": 2 1 3
>
> Notice - the order of factor levels for xx is not 1 2 3 as it should
> be but 2 1 3. How come?
>
> Or also look at this:
>>test$xx
> [1] 9  3  15
> Levels: 3 9 15
>
> Same thing.
> Do you know what might be the reason?
>
> Thank you very much!
>
> --
> Dimitri Liakhovitski
> MarketTools, Inc.
> Dimitri.Liakhovitski at markettools.com
>
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>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?