[R] extracting rows of a dataframe

[Petr Pikal]

Hi

or maybe 

 x <- as.numeric(a[2,-1])

can suit to your needs.

Petr




On 2 Dec 2005 at 17:14, Berwin A Turlach wrote:

From:           	Berwin A Turlach <berwin at maths.uwa.edu.au>
Date sent:      	Fri, 2 Dec 2005 17:14:42 +0800
To:             	Robin Hankin <r.hankin at noc.soton.ac.uk>
Copies to:      	RHelp <r-help at stat.math.ethz.ch>
Subject:        	Re: [R] extracting rows of a dataframe
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> >>>>> "RH" == Robin Hankin <r.hankin at noc.soton.ac.uk> writes:
> 
>     RH> Three questions:
> 
>     RH> (1)  why is as.vector(a[2,-1]) not a vector?
> Did you read the help file of as.vector() ?
> 
> > a <- data.frame(male=c(T,T,F),mass=c(1,4,3),height=c(4,3,2))
> > a
>    male mass height
> 1  TRUE    1      4
> 2  TRUE    4      3
> 3 FALSE    3      2
> > x <- as.vector(a[2,-1])
> > mode(x)
> [1] "list"
> > str(x)
> `data.frame':	1 obs. of  2 variables:
>  $ mass  : num 4
>  $ height: num 3
> 
> Clearly you want:
> 
> > x <- as.vector(a[2,-1], mode="numeric")
> > str(x)
>  num [1:2] 4 3
> > x
> [1] 4 3
> 
> 
>     RH> (2) How come setting names to NULL gives me bad weirdness? >
> names(x) <- NULL > str(x) `data.frame':	1 obs. of  2 variables:
>  $ : num 4
>  $ : num 3
> > x
>   structure("4", class = "AsIs") structure("3", class = "AsIs")
> 2                              4                              3
> 
> With your "names(x)<-NULL" command you are wiping out the names of the
> variables in your data frame.  Looking at print.data.frame(), the
> answer to the so-called weirdness can presumably be found in
> format.data.frame(). 
> 
>     RH> (3) Can I structure my dataframe in a better way, so that RH>
>     this problem does not occur?
> Not really, it's more a question of the appropriate use of
> as.vector(). :-))
> 
> Cheers,
> 
>         Berwin
> 
> ========================== Full address ============================
> Berwin A Turlach                      Tel.: +61 (8) 6488 3338 (secr)  
> School of Mathematics and Statistics        +61 (8) 6488 3383 (self)  
>    The University of Western Australia   FAX : +61 (8) 6488 1028 35
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> e-mail: berwin at maths.uwa.edu.au Australia                       
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> 
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Petr Pikal
petr.pikal at precheza.cz