[R] Different behavior of median and mean function - Why?

[Christoph Jäckel]

Hey together,

thanks a lot for the quick and helpful answers. I will not use median
on a data.frame from now on and use sapply instead.

Thanks Christoph

On Thu, May 26, 2011 at 11:37 PM, Marc Schwartz <marc_schwartz at me.com> wrote:
> On May 26, 2011, at 4:22 PM, Christoph Jäckel wrote:
>
>> Hi together,
>>
>> below is a small example which produces outcome I do not understand,
>> namely that the median function works fine on a data.frame without
>> negative numbers, but doesn't work on a data.frame with one negative
>> number. I'm sure there is a reasonable explanation for that or better,
>> that I'm doing something wrong and someone could guide me how to solve
>> it. I tried googling it, but couldn't find a solution:
>>
>>> #Set up data frame
>>> df <- data.frame(V1=c(1,2,3,4),V2=c(2,3,4,5))
>>> #Both work fine
>>> mean(df)
>> V1  V2
>> 2.5 3.5
>>> median(df)
>> [1] 2.5 3.5
>>>
>>> #Now, I just make one number negative in the data.frame
>>> df <- data.frame(V1=c(1,2,3,-4),V2=c(2,3,4,5))
>>> mean(df)#Works fine
>> V1  V2
>> 0.5 3.5
>>> median(df)#Why do I  get that error?
>> [1]  NA 0.5
>> Warnmeldung:
>> In mean.default(X[[1L]], ...) :
>>  argument is not numeric or logical: returning NA
>>> #It works fine on both columns seperately
>>> median(df$V1)
>> [1] 1.5
>>> median(df$V2)
>> [1] 3.5
>
>
> This was actually just discussed late last month. See the thread here:
>
>  https://stat.ethz.ch/pipermail/r-devel/2011-April/060731.html
>
> The bottom line is that median does not have a 'method' for data frames, whereas mean does.
>
> HTH,
>
> Marc Schwartz
>
>



-- 
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Christoph Jäckel (Dipl.-Kfm.)

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Research Assistant

Chair for Financial Management and Capital Markets | Lehrstuhl für
Finanzmanagement und Kapitalmärkte

TUM School of Management | Technische Universität München

Arcisstr. 21 | D-80333 München | Germany

Mailto: christoph.jaeckel at wi.tum.de | Web: www.fm.wi.tum.de

Phone: +49 89 289 25482 | Fax: +49 89 289 25488



Head of Chair:

Univ.-Prof. Dr. Christoph Kaserer

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