[R] [External] Convert a character string to variable names

[Bert Gunter]

Yes, I said that Rui. If she is really just trying to extract equal length
columns from a data frame or list by names(as strings), as I said,  then
none of this is necessary:
as.matrix(mtcars[, x])  ## does it

Or have I missed something?

Bert

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Mon, Feb 7, 2022 at 3:36 PM Rui Barradas <ruipbarradas using sapo.pt> wrote:

> Hello,
>
> But that doesn't work in the OP's case:
>
>
> sapply(.x, get)
> #Error in FUN(X[[i]], ...) : object 'mtcars$disp' not found
>
>
> Like you say, as.name(x$something) is not the name of an object.
>
> Hope this helps,
>
> Rui Barradas
>
> Às 23:21 de 07/02/2022, Bert Gunter escreveu:
> > I assume that the mtcars components were used only as an example, as you
> > could convert them to a matrix via as.matrix(). Unfortunately, it was a
> bad
> > choice: as.name("x$something") is not the name of 'something' in the
> data
> > frame (or list) x. Moreover, as.name("x") does not point to an object x
> --
> > as Rich indicated, it has to be evaluated to do so.
> >> x<- 1:10
> >> z <- as.name("x")
> >> z
> > x
> >> length(z)
> > [1] 1
> >> eval(z)
> >   [1]  1  2  3  4  5  6  7  8  9 10
> >
> > But more to the point, I think you are attempting to drive from Brooklyn
> to
> > New York City by way of Los Angeles. If I understand correctly, I think
> all
> > you need is ?get:
> >
> >> x <- runif(5)
> >> y <- 1:5
> >> z <- 21:25
> >> nm <- c('x', 'y','z')
> >> sapply(nm, get)
> >                x y  z
> > [1,] 0.99602479 1 21
> > [2,] 0.97458756 2 22
> > [3,] 0.09496625 3 23
> > [4,] 0.91444550 4 24
> > [5,] 0.68331484 5 25
> >
> > Cheers,
> > Bert Gunter
> >
> > "The trouble with having an open mind is that people keep coming along
> and
> > sticking things into it."
> > -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
> >
> >
> > On Mon, Feb 7, 2022 at 3:06 PM Richard M. Heiberger <rmh using temple.edu>
> wrote:
> >
> >>> x <- c("mtcars$disp", "mtcars$hp", "mtcars$cyl")
> >>> x
> >> [1] "mtcars$disp" "mtcars$hp"   "mtcars$cyl"
> >>> eval(parse(text=x))
> >>   [1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4
> >>> for (i in x) print(eval(parse(text=i)))
> >>   [1] 160.0 160.0 108.0 258.0 360.0 225.0 360.0 146.7 140.8 167.6 167.6
> >> 275.8 275.8 275.8 472.0 460.0 440.0  78.7  75.7  71.1 120.1 318.0
> >> [23] 304.0 350.0 400.0  79.0 120.3  95.1 351.0 145.0 301.0 121.0
> >>   [1] 110 110  93 110 175 105 245  62  95 123 123 180 180 180 205 215
> 230
> >> 66  52  65  97 150 150 245 175  66  91 113 264 175 335 109
> >>   [1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4
> >>
> >>
> >>> On Feb 07, 2022, at 17:55, Erin Hodgess <erinm.hodgess using gmail.com>
> wrote:
> >>>
> >>>> .x
> >>>
> >>> [1] "mtcars$disp" "mtcars$hp"   "mtcars$cyl"
> >>
> >> ______________________________________________
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> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>

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