extracting rows of a dataframe

"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

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