# [R] Define pch and color based on two different columns

Peter Langfelder peter@|@ng|e|der @end|ng |rom gm@||@com
Wed Apr 10 06:36:48 CEST 2019

Sorry for being late to the party, but has anyone suggested a minor
but important modification of the code from stack exchange?

xyplot(mpg ~ wt | cyl,
panel = function(x, y, ..., groups, subscripts) {
pch <- mypch[factor(carb)[subscripts]]
col <- mycol[factor(gear)[subscripts]]
grp <- c(gear,carb)
panel.xyplot(x, y, pch = pch, col = col)
}
)

>From the little I understand about what you're trying to do, this may
just do the trick.

Peter

On Tue, Apr 9, 2019 at 2:43 PM Matthew Snyder <msnyder424 using gmail.com> wrote:
>
> I am making a lattice plot and I would like to use the value in one column
> to define the pch and another column to define color of points. Something
> like:
>
> xyplot(mpg ~ wt | cyl,
>        data=mtcars,
>        col = gear,
>        pch = carb
> )
>
> There are unique pch points in the second and third panels, but these
> points are only unique within the plots, not among all the plots (as they
> should be). You can see this if you use the following code:
>
> xyplot(mpg ~ wt | cyl,
>        data=mtcars,
>        groups = carb
> )
>
> This plot looks great for one group, but if you try to invoke two groups
> using c(gear, carb) I think it simply takes unique combinations of those
> two variables and plots them as unique colors.
>
> Another solution given by a StackExchange user:
>
> mypch <- 1:6
> mycol <- 1:3
>
> xyplot(mpg ~ wt | cyl,
>           panel = function(x, y, ..., groups, subscripts) {
>               pch <- mypch[factor(carb[subscripts])]
>               col <- mycol[factor(gear[subscripts])]
>               grp <- c(gear,carb)
>               panel.xyplot(x, y, pch = pch, col = col)
>           }
> )
>
> This solution has the same problems as the code at the top. I think the
> issue causing problems with both solutions is that not every value for each
> group is present in each panel, and they are almost never in the same
> order. I think R is just interpreting the appearance of unique values as a
> signal to change to the next pch or color. My actual data file is very
> large, and it's not possible to sort my way out of this mess. It would be
> best if I could just use the value in two columns to actually define a
> color or pch for each point on an entire plot. Is there a way to do this?
>
> Ps, I had to post this via email because the Nabble site kept sending me an
> error message: "Message rejected by filter rule match"
>
> Thanks,
> Matt
>
>
>
> *Matthew R. Snyder*
> *~~~~~~~~~~~~~~~~~*
> PhD Candidate
> University Fellow
> University of Toledo
> Computational biologist, ecologist, and bioinformatician
> Sponsored Guest Researcher at NOAA PMEL, Seattle, WA.
> Matthew.Snyder6 using rockets.utoledo.edu
> MSnyder424 using gmail.com
>
>
>
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