[R] Re: R-help Digest, Vol 24, Issue 28

[John Maindonald]

You've omitted a comma. races2000 is a data frame,
which for purposes of extracting rows behaves like
a 2-dimenional object.  The following works fine:

   hills2000 <- races2000[races2000$type == 'hill', ]

Additionally, you might like to ponder
   > type <- races2000[names(races2000)=="type"]
   > type[1:4]
   Error in "[.data.frame"(type, 1:4) : undefined columns selected
   > length(type)                  # type is a data frame with 1 column
   [1] 1
   > vtype <- unlist(type)    # Extract the vector that is the one
                                              # data frame (list) element
   > vtype[1:4]                      # Try also length(vtype)
   type.type1 type.type2 type.type3 type.type4
     "uphill"    "other"    "other"    "relay"

Your syntax (without the comma) does give a result,
providing that the dimensions match (the condition must
have the same number of elements as races2000 has
columns), but it is probably not the result that you want!
See further pp.320-321 of the DAAG book.

John Maindonald             email: john.maindonald at anu.edu.au
phone : +61 2 (6125)3473    fax  : +61 2(6125)5549
Centre for Bioinformation Science, Room 1194,
John Dedman Mathematical Sciences Building (Building 27)
Australian National University, Canberra ACT 0200.

On 28 Feb 2005, at 10:07 PM, r-help-request at stat.math.ethz.ch wrote:

> From: Clint Harshaw <charshaw at presby.edu>
> Date: 28 February 2005 1:08:36 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] subsetting data set dimenion problem
>
>
> (See DAAG book, p. 173, ex. 3)
>
> I'm a new user of R, and I'm following the DAAG text. I want to create 
> a subset of the races2000 data frame, but get errors because of a 
> mismatch of values in some columns:
>
> > library(DAAG)
> > attach(races2000)
> > hills2000 <- races2000[races2000$type == 'hill']
> Error in as.matrix.data.frame(x) : dim<- : dims [product 770] do not 
> match the length of object [771]
>
> However, if I follow the solution given, and remove redundant columns 
> 1 through 6 and column 11 (which I won't need, since I know they are 
> going to have the same value), I don't get the error:
>
> > hills2000 <- races2000[races2000$type == 'hill', -c(1:6,11)]
> > hills2000
>                        dist climb      time      timef
> Tiso Carnethy          6.00  2500 0.7822222  0.9191667
> [...]
> Cornalees              5.50   800 0.6183333         NA
> [...]
>
> What is causing the error with my original subsetting? I speculated it 
> was related to the NA values, but there is an NA in the resulting 
> hills2000, corresponding to the Cornalees hill race.
>
> Thanks,
> Clint
> -- 
> Clint Harshaw, PhD		
> Department of Mathematics
> Presbyterian College
> Clinton SC  29325
>
> EMail: charshaw at presby.edu	
> Phone: 864.833.8995
> Fax: 864.938.3769
> Office: Harrington-Peachtree Rm 412
>
John Maindonald             email: john.maindonald at anu.edu.au
phone : +61 2 (6125)3473    fax  : +61 2(6125)5549
Centre for Bioinformation Science, Room 1194,
John Dedman Mathematical Sciences Building (Building 27)
Australian National University, Canberra ACT 0200.