[R] Confused about using data.table package,

C W tmrsg11 at gmail.com
Tue Feb 21 03:53:29 CET 2017


Thanks Hadley!

While I got your attention, what is a good way to get started on ggplot2? ;)

My impression is that I first need to learn plyr, dplyr, AND THEN ggplot2.
That's A LOT!

Suppose i have this:
iris
iris2 <- cbind(iris, grade = sample(1:5, 150, replace = TRUE))
iris2

I want to have some kind of graph conditioned on species, by grade . What's
a good lead to learn about plotting this?

Thank you!



On Mon, Feb 20, 2017 at 11:12 AM, Hadley Wickham <h.wickham at gmail.com>
wrote:

> On Sun, Feb 19, 2017 at 3:01 PM, David Winsemius <dwinsemius at comcast.net>
> wrote:
> >
> >> On Feb 19, 2017, at 11:37 AM, C W <tmrsg11 at gmail.com> wrote:
> >>
> >> Hi R,
> >>
> >> I am a little confused by the data.table package.
> >>
> >> library(data.table)
> >>
> >> df <- data.frame(w=rnorm(20, -10, 1), x= rnorm(20, 0, 1), y=rnorm(20,
> 10, 1),
> >> z=rnorm(20, 20, 1))
> >>
> >> df <- data.table(df)
> >
> >   df <- setDT(df) is preferred.
>
> Don't you mean just
>
> setDT(df)
>
> ?
>
> setDT() modifies by reference.
>
> >>
> >> df_3 <- df[, a := x-y] # created new column a using x minus y, why are
> we
> >> using colon equals?
> >
> > You need to do more study of the extensive documentation. The behavior
> of the ":=" function is discussed in detail there.
>
> You can get to that documentation with ?":="
>
> Hadley
>
> --
> http://hadley.nz
>

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