[R] select subsets in data frame

[Chuck Cleland]

Mark Hempelmann wrote:
> Dear WizaRds!
> 
> A trivial question indeed on selecting subsets in data frames. I am 
> sorry. Unfortunately, I did not find any helpful information on the 
> introduction, searched the help archive and read in introductory books. 
> Please help:
> 
> I want to select column "KB" which is read via read.csv2 as a data.frame 
> into d. I checked that it is indeed a data.frame object and included the 
> correct header information in line 1. For example purposes, look at this 
> small object:
> <<*>>= (4)
> d <- data.frame(A=1:3, Date=c("01.01.07","02.01.07","03.01.07"),
> KB=c("Eenie", "Meenie", "Miney") )
> 
> d["KB"=="Eenie",] # gives
> @
> output-start
> [1] A    Date KB
> <0 rows> (or 0-length row.names)
> output-end
> @

  Try this instead:

subset(d, KB == "Eenie")

  A     Date    KB
1 1 01.01.07 Eenie

?subset

> If I follow Venables/ Ripley in Modern Applied Statistics with S, it 
> should look like this:
> 
> <<*>>= (5)
> library(MASS)
> attach(painters)
> painters[Colour>=17,]
> @
> gives the correct subset. But
> d[KB=="Eenie",] # gives
> 
> Error in `[.data.frame`(d, KB == "Eenie", ) :
>          object "KB" not found

  Works for me if I attach the data frame first:

attach(d)

d[KB == "Eenie",]

  A     Date    KB
1 1 01.01.07 Eenie

> I need every KB named Eenie. What did I do wrong? The alternative I 
> found seems to be quite complicated:
> 
> <<*>>= (6)
> d[which( d[,"KB"]=="Eenie" ), ]
> @
> output-start
>    A     Date    KB
> 1 1 01.01.07 Eenie
> output-end
> 
> Thank you so much for your help.
> 
> cheers
> mark
> 
> 
> "I believe I found the missing link between animal and civilized man. 
> It's us." -- Konrad Lorenz
> 
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-- 
Chuck Cleland, Ph.D.
NDRI, Inc.
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