[R] dataframe subset using levels as criteria

[Prof Brian Ripley]

On 30 Jan 2002, Ernesto Jardim wrote:

> Hi
>
> I want to select a subset of a dataframe (frota) using the levels of a
> factor (matricula) in another dataframe (logbooks.eda).
>
> The command and output are bellow and it's not working ...
>
> > frota[frota$matricula==levels(logbooks.eda$matricula),]
>   matricula compff   tab potmaq
> 1  A-1420-C     NA    NA     NA
> 2  A-1676-C     NA 12070  36800
> 3  A-1954-C   3214 17565  44100
> 4  A-1961-C   3197 17992  46300
> 5  A-2011-C   3198 17184  46300
> Warning messages:
> 1: longer object length
> 	is not a multiple of shorter object length in: is.na(e1) | is.na(e2)
> 2: longer object length
> 	is not a multiple of shorter object length in:
> "==.default"(frota$matricula, levels(logbooks.eda$matricula))
>
> Can someone help me with this ?

Use %in% and not ==.  == matches cyclically along the shorter vector, and
I presume you want all cases matching any of the levels.

-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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