Re: [R] Getting subsets of a data frame

From: Fernando Saldanha <fsaldan1_at_gmail.com>
Date: Sat 16 Apr 2005 - 21:53:25 EST

Thanks, it's interesting reading.

I also noticed that

sw[, 1, drop = TRUE] is a vector (coerces to the lowest dimension)

but

sw[1, , drop = TRUE] is a one-row data frame (does not convert it into a list or vector)

FS

On 4/16/05, Bill.Venables@csiro.au <Bill.Venables@csiro.au> wrote:
> You should look at
>
> > ?"["
>
> and look very carefully at the "drop" argument. For your example
>
> > sw[, 1]
>
> is the first component of the data frame, but
>
> > sw[, 1, drop = FALSE]
>
> is a data frame consisting of just the first component, as
> mathematically fastidious people would expect.
>
> This is a convention, and like most arbitrary conventions it can be very
> useful most of the time, but some of the time it can be a very nasty
> trap. Caveat emptor.
>
> Bill Venables.
>
> -----Original Message-----
> From: r-help-bounces@stat.math.ethz.ch
> [mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Fernando Saldanha
> Sent: Saturday, 16 April 2005 1:07 PM
> To: Submissions to R help
> Subject: [R] Getting subsets of a data frame
>
> I was reading in the Reference Manual about Extract.data.frame.
>
> There is a list of examples of expressions using [ and [[, with the
> outcomes. I was puzzled by the fact that, if sw is a data frame, then
>
> sw[, 1:3]
>
> is also a data frame,
>
> but
>
> sw[, 1]
>
> is just a vector.
>
> Since R has no scalars, it must be the case that 1 and 1:1 are the same:
>
> > 1 == 1:1
> [1] TRUE
>
> Then why isn't sw[,1] = sw[, 1:1] a data frame?
>
> FS
>
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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sat Apr 16 22:36:12 2005

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