[R] x[x$a=="q",,drop=TRUE]

[Francisco J. Zagmutt]

the argument drop =TRUE is not meant to do that (see several responses from 
Peter Dalgaard about this issue i.e. 
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/37333.html)

If you want to drop unused factor levels try:

sprayS$PD<-factor(sprayS$PD)


Cheers

Francisco

>From: Mikkel Grum <mi2kelgrum at yahoo.com>
>To: RHelp <r-help at stat.math.ethz.ch>
>Subject: [R] x[x$a=="q",,drop=TRUE]
>Date: Wed, 1 Jun 2005 11:08:46 -0700 (PDT)
>
>I'm trying to select a subset of a dataframe while
>dropping some factors. While the dataset gets smaller
>all Factor levels remain and I need to get rid of
>them.  Strangely enough, I am almost certain that the
>same code on the same data worked OK earlier today -
>and it is not the first time that I'm not able to
>replicate earlier results with this command (I know, I
>might just be going crazy). What am I doing wrong?
>
>I'm working on Windows Server 2003, R 2.1.0
>(2005-04-18).
>
> > str(spray)
>`data.frame':   370 obs. of  7 variables:
>  $ PD        : Factor w/ 8 levels
>"Botrytis","Downy",..: 2 2 2 2 4 2 2 5 5 5 ...
>  $ postSpmtsQ: num  1309 1309  384  384 1044 ...
>  $ ante62Q   : num  284 284 218 218 366 ...
>  $ ante08Q   : num  331 331 228 228 492 ...
>  $ ante29Q   : num   297  297 1067 1067 1034 ...
>  $ ante16Q   : num  0 0 0.2 0.2 0 0 0 6.7 0 31.5 ...
>  $ Trt       : Factor w/ 41 levels "Acrobat MZ WP",..:
>27 5 27 5 36 27 5 24 24 24 ...
> > sprayS <- spray[spray$PD == "Spidermites", , drop =
>TRUE]
> > str(sprayS)
>`data.frame':   111 obs. of  7 variables:
>  $ PD        : Factor w/ 8 levels
>"Botrytis","Downy",..: 5 5 5 5 5 5 5 5 5 5 ...
>  $ postSpmtsQ: num  13395 31588 84254   136   619 ...
>  $ ante62Q   : num   1357 21187 21819   218   237 ...
>  $ ante08Q   : num    973 21740 25112   228   134 ...
>  $ ante29Q   : num    2103 106970  66676   1067    119
>...
>  $ ante16Q   : num  6.7 0 31.5 0.2 0 0 0 0 14.3 0 ...
>  $ Trt       : Factor w/ 41 levels "Acrobat MZ WP",..:
>24 24 24 24 24 24 24 24 24 24 ...
> > table(sprayS$Trt)
>
>     Acrobat MZ WP           Agrifos      Apollo 50 SC
>           CALMAG
>                 0                 0                13
>                0
>             DM-31    Dynamec 1.8 EC   Equation Pro DF
>        Evisect S
>                 0                13                 0
>                0
>             Flint         Floramite           Impulse
>           Karate
>                 0                15                 0
>                0
>       Karate zeon            Melody    Meltatox 40 EC
>              MKP
>                 0                 0                 0
>                0
>          Molasses       Nembicidine     Nimrod 250 EC
>   Nissorun 10 EC
>                 0                 0                 0
>               12
>            Oberon     Orthene 75 WP       Oscar 20 SC
>          Pegasus
>                15                 0                 9
>               26
>      Polar 50 WSG            Potfos          Proplant
>            Pyrus
>                 0                 0                 0
>                0
>Ridomil MZ 63 5WP   Rovral aqua flo      Score 250 EC
>     Secure 36 SC
>                 0                 0                 0
>                8
>       Sequestrone          Shavit f         Sporekill
>     Stroby 50 WG
>                 0                 0                 0
>                0
>            Switch            Tracer          Trafos K
>         Vandozeb
>                 0                 0                 0
>                0
>           Vitomex
>                 0
>
>cheers,
>Mikkel
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide! 
>http://www.R-project.org/posting-guide.html