[R] extracting rows of a dataframe

[Patrick Burns]

The key things here are:

1) a data frame is a list with some attributes (unlike a
matrix which is (generally) an atomic vector with attributes).

2) 'as.vector' removes attributes.

Patrick Burns
patrick at burns-stat.com
+44 (0)20 8525 0696
http://www.burns-stat.com
(home of S Poetry and "A Guide for the Unwilling S User")

Robin Hankin wrote:

>Hi
>
>look at the following session, in which I have a dataframe,
>and I want to extract the second row, without the first column.
>
>Everything works as expected until the last line, where I set
>the names of x to NULL, and get a non-desired object (I
>want c(4,3).).
>
>
>Three questions:
>
>(1)  why is as.vector(a[2,-1]) not a vector?
>
>(2) How come setting names to NULL gives me bad weirdness?
>
>(3) Can I structure my dataframe in a better way, so that
>this problem does not occur?
>
>
>
>
> > 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])
> > x
>   mass height
>2    4      3
> > names(x) <- NULL
> > x
>   structure("4", class = "AsIs") structure("3", class = "AsIs")
>2                              4                              3
> >
>
>--
>Robin Hankin
>Uncertainty Analyst
>National Oceanography Centre, Southampton
>European Way, Southampton SO14 3ZH, UK
>  tel  023-8059-7743
>
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