[R] Problem with subset() function?

[Andrew Robinson]

Steven,

check the class of the objects that you are creating.

Cheers,

Andrew

On Wed, January 21, 2009 10:02 am, Steven McKinney wrote:
> Hi all,
>
> Can anyone explain why the following use of
> the subset() function produces a different
> outcome than the use of the "[" extractor?
>
> The subset() function as used in
>
>  density(subset(mydf, ht >= 150.0 & wt <= 150.0, select = c(age)))
>
> appears to me from documentation to be equivalent to
>
>  density(mydf[mydf$ht >= 150.0 & mydf$wt <= 150.0, "age"])
>
> (modulo exclusion of NAs) but use of the former yields an
> error from density.default() (shown below).
>
>
> Is this a bug in the subset() machinery?  Or is it
> a documentation issue for the subset() function
> documentation or density() documentation?
>
> I'm seeing issues such as this with newcomers to R
> who initially seem to prefer using subset() instead
> of the bracket extractor.  At this point these functions
> are clearly not exchangeable.  Should code be patched
> so that they are, or documentation amended to show
> when use of subset() is not appropriate?
>
>> ### Bug in subset()?
>
>> set.seed(123)
>> mydf <- data.frame(ht = 150 + 10 * rnorm(100),
> +                    wt = 150 + 10 * rnorm(100),
> +                    age = sample(20:60, size = 100, replace = TRUE)
> +                    )
>
>
>> density(subset(mydf, ht >= 150.0 & wt <= 150.0, select = c(age)))
> Error in density.default(subset(mydf, ht >= 150 & wt <= 150, select =
> c(age))) :
>   argument 'x' must be numeric
>
>
>> density(mydf[mydf$ht >= 150.0 & mydf$wt <= 150.0, "age"])
>
> Call:
> 	density.default(x = mydf[mydf$ht >= 150 & mydf$wt <= 150, "age"])
>
> Data: mydf[mydf$ht >= 150 & mydf$wt <= 150, "age"] (29 obs.);	Bandwidth
> 'bw' = 5.816
>
>        x                y
>  Min.   : 4.553   Min.   :3.781e-05
>  1st Qu.:22.776   1st Qu.:3.108e-03
>  Median :41.000   Median :1.775e-02
>  Mean   :41.000   Mean   :1.370e-02
>  3rd Qu.:59.224   3rd Qu.:2.128e-02
>  Max.   :77.447   Max.   :2.665e-02
>
>
>> sessionInfo()
> R version 2.8.0 Patched (2008-11-06 r46845)
> powerpc-apple-darwin9.5.0
>
> locale:
> C
>
> attached base packages:
> [1] stats     graphics  grDevices datasets  utils     methods   base
>
> loaded via a namespace (and not attached):
> [1] Matrix_0.999375-16 grid_2.8.0         lattice_0.17-15
> lme4_0.99875-9
> [5] nlme_3.1-89
>>
>
>
>
>
>
>
> Steven McKinney
>
> Statistician
> Molecular Oncology and Breast Cancer Program
> British Columbia Cancer Research Centre
>
> email: smckinney +at+ bccrc +dot+ ca
>
> tel: 604-675-8000 x7561
>
> BCCRC
> Molecular Oncology
> 675 West 10th Ave, Floor 4
> Vancouver B.C.
> V5Z 1L3
> Canada
>
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>


Andrew Robinson
Senior Lecturer in Statistics                       Tel: +61-3-8344-6410
Department of Mathematics and Statistics            Fax: +61-3-8344 4599
University of Melbourne, VIC 3010 Australia
Email: a.robinson at ms.unimelb.edu.au    Website: http://www.ms.unimelb.edu.au