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

[Tae-Hoon Chung]

Hi, Mikkel;

The problem here, I think, is that spray$PD is NOT recognized as character
in R. Actually, R understands it as factors according to your printout. This
happens quite a lot if you use read.table and come across characters within
the data file. One remedy I use often use is doing something like

spray$PD <- as.character(spray$PD)

to make it sure that spray$PD is character.

Tae-Hoon Chung
--------------------------------------------------
Tae-Hoon Chung
Post-Doctoral Researcher
Translational Genomics Research Institute (TGen)
445 N. 5th Street (Suite 530)
Phoenix, AZ 85004
1-602-343-8724 (Direct)
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1-602-343-8840 (Fax)
--------------------------------------------------



On 6/1/05 11:08 AM, "Mikkel Grum" <mi2kelgrum at yahoo.com> wrote:

> 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
> 
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