[R] expression in lattice panel strip

[Deepayan Sarkar]

This is possible but a little cumbersome. Bert is on the right track with
strip.custom:

xyplot(ts(cbind(x1 = cs, x2 = cs + w)),
       strip = strip.custom(factor.levels =
                                expression(2 * cos(2 * pi * t / 50 + 0.6 *
pi),
                                           2 * cos(2 * pi * t / 50 + 0.6 *
pi) + N(0, 1))),
       type = c("l", "g"),
       main = expression(2 * cos(2 * pi * t / 50 + 0.6 * pi)))

where (from the docs):

factor.levels: vector of character strings or expressions giving the
          levels of the conditioning variable currently being drawn.
          For more than one conditioning variable, this will vary with
          'which.given'.

This is relatively straightforward with only one conditioning variable. A
more general solution for multiple conditioning variables would be

estrip <- function(..., factor.levels)
{
    strip.default(..., factor.levels = parse(text = factor.levels))
}

xyplot(ts(cbind(x1 = cs, x2 = cs + w)),
       screens = list(x1 = "2 * cos(2 * pi * t / 50 + 0.6 * pi)",
                      x2 = "2 * cos(2 * pi * t / 50 + 0.6 * pi) + N(0, 1)"),
       strip = estrip,
       type = c("l", "g"),
       main = expression(2 * cos(2 * pi * t / 50 + 0.6 * pi)))

Best,
-Deepayan

On Mon, 3 Mar 2025 at 06:38, Bert Gunter <bgunter.4567 using gmail.com> wrote:

> Full disclosure: I have never plotted time series using this xyplot method.
>
> However, ?xyplot.ts says:
>
> "screens
>
> factor (or coerced to factor) whose levels specify which panel each
> series is to be plotted in. screens = c(1, 2, 1) would plot series 1,
> 2 and 3 in panels 1, 2 and 1. May also be a named list, see Details
> below."
>
> From that I would infer the answer to your query in no: factors, know
> nothing about plotmath notation, and as.factor() just coerces your
> expressions to character strings that are the factor labels.
> strip.default() then uses these character strings as the labels for
> the strips, giving what you got.
>
> As you only want to use a "pi" character, 𝛑, in your math expression,
> I tried using a UTF-8 symbol for it, \U1D6D1, in quoted strings as the
> argument for the screens parameter. That is:
>
> striplabs <- factor(c("2cos(2\U1D6D1t/50 + 0.6\U1D6D1)",
>                       "2cos(2\U1D6D1t /50 + 0.6\U1D6D1) + N(0, 1)"))
> xyplot(ts(cbind(x1 = cs, x2 = cs + w)),
>        type = c("l", "g"),
>        main = expression(2 * cos(2 * pi * t / 50 + 0.6 * pi)),
>        screens = striplabs
> )
>
> The RStudio graphics device was *not* able to interpret the UTF-8 in
> the strip, but on my Mac, the Cairo_pdf() device (or just using the
> export button to export the graphic as a pdf from RStudio) *did*
> reproduce the characters nicely in the strip labels in the pdf.
> Unfortunately, the main title expression symbol for pi (presumably
> from the adobe font symbols) did not look nice. However, using the
> quoted graphics string (the first level of the striplabs factor) does
> fine, of course.
>
> As I just sort of barely know what I'm doing here, there may be a much
> better way to do this by using an appropriate font specification in a
> strip = strip.custom(par.strip.text= ...) argument to xyplot, but that
> exceeds my current abilities. Maybe you or one of the R cognescenti
> can figure it  out.
>
> Again, please note my full disclosure.
>
> Cheers,
> Bert
>
> "An educated person is one who can entertain new ideas, entertain
> others, and entertain herself."
>
> "An educated person is one who can entertain new ideas, entertain
> others, and entertain herself."
>
>
>
> On Sun, Mar 2, 2025 at 6:56 AM Naresh Gurbuxani
> <naresh_gurbuxani using hotmail.com> wrote:
> >
> > Is it possible to include expression in lattice panel strip?
> > Thanks,
> > Naresh
> >
> > cs <- 2 * cos(2 * pi * (1:500) / 50 + 0.6 * pi)
> > w <- rnorm(500)
> > xyplot(ts(cbind(x1 = cs, x2 = cs + w)), screens = list(x1 = expression(2
> * cos(2 * pi * t / 50 + 0.6 * pi)), x2 = expression(2 * cos(2 * pi * t / 50
> + 0.6 * pi) + N(0, 1))), type = c("l", "g"), main = expression(2 * cos(2 *
> pi * t / 50 + 0.6 * pi)))
> >
> > # Greek letter pi is shown in main title, but not in panel strips
> > ______________________________________________
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> https://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> 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
> https://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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