[R] [External] add equation and rsqared to plot

[Bill Dunlap]

plotmath also accepts names and calls, which it treats as though they were
single-element expressions.  That is why quote() generally works.
quote("string") or quote(123) does not invoke plotmath, as quote returns a
literal string or number when given such a thing.

plot(0:1,0:1,type="n")
text(.2, .6, expression(phi^epsilon))
text(.2, .4, quote(phi^epsilon))
text(.7, .6, expression(1234567890123456))
text(.7, .4, quote(1234567890123456))

-Bill

On Fri, Apr 8, 2022 at 9:49 AM Bert Gunter <bgunter.4567 using gmail.com> wrote:

> Yes, I also find it somewhat confusing. Perhaps this will help. I
> apologize beforehand if I have misunderstood and you already know all
> this.
>
> The key is to realize that plotmath works with **expressions**,
> unevaluated forms that include special plotmath keywords, like 'atop',
> and symbols. So...
>
> ## simple example with plotmath used in plot's title
>
> ## This will produce an error, as 'atop' is not an R function:
> plot(1,1, main = atop(x,y))
>
> ## to make this work, we need an expression on the rhs of 'main =' . A
> simple way to do this is to use quote():
>
> plot(1,1,main = quote(atop(x,y)))
>
> ## Note that this produce 'x' above 'y' **without quoting x and y**.
> That's because
> ## this is an expression that plotmath parses and evaluates according
> to its own rules,
> ## shown in ?plotmath
>
> ## Now suppose we have:
> x <- 'first line'
> y <- 'second line'
>
> ## and we want to display these quoted strings instead of 'x' and 'y'
> in the title
>
> ## Then this will *not* work -- it gives the same result as before:
> plot(1,1,main = quote(atop(x,y)))
>
> ## So what is needed here is R's 'computing on the language"
> capability to substitute
> ## the quoted strings for x and y in the expression. Here are two
> simple ways to do this:
>
> ## First using substitute()
>
> plot(1,1, main = substitute(atop(x,y), list (x =x, y = y)))
>
> ## Second, using bquote()
>
> plot(1,1, main = bquote(atop(.(x), .(y))))
>
> ## More complicated expressions can be built up using plotmath's rules.
> ## But you need to be careful about distinguishing plotmath expressions and
> ## ordinary R expressions. For example:
>
> x <- pi/4  ## a number
>
> ## WRONG -- will display as written. bquote() is the same as quote() here.
> plot(1,1, main = bquote(sin(pi/4) == round(x,2)))
>
> ## WRONG -- will substitute value of x rounded to session default
> ## in previous. This is a mistake in using bquote
> plot(1,1, main = bquote(sin(pi/4) == round(.(x), 2)))
>
> ## RIGHT -- use of bquote
> plot(1,1, main = bquote(sin(pi/4) == .(round(x,2))))
> ## or -- using substitute
> plot(1,1, main = substitute(sin(pi/4) == x, list(x = round(x,2))))
>
> Hope this is helpful and, again, apologies if I have misunderstood.
>
> 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 Fri, Apr 8, 2022 at 7:42 AM PIKAL Petr <petr.pikal using precheza.cz> wrote:
> >
> > Hallo David
> >
> > Fair enough. Thanks for your explanation, which told me what should be
> done. It works perfectly for my example but I am still confused how to get
> expressions given to atop (or other functions) be evaluated and help page
> does not enlighten me, so I am still puzzled.
> >
> > When I borrow example from help,
> >
> > plot(1:10, type="n", xlab="", ylab="", main = "plot math & numbers")
> > theta <- 1.23 ; mtext(bquote(hat(theta) == .(theta)), line= .25)
> > for(i in 2:9)
> >     text(i, i+1, substitute(list(xi, eta) == group("(",list(x,y),")"),
> >                             list(x = i, y = i+1)))
> >
> > #this is OK
> > ex1 <- expression("      first: {f * minute}(x) " == {f * minute}(x))
> > ex2 <- expression("               second: {f * second}(x) "        == {f
> * second}(x))
> > text(1, 9.6, ex1, adj=0)
> > text(1, 9.0, ex2, adj=0)
> >
> > #and this is not
> > text(2, 8, expression(atop(ex1, ex2)))
> > text(2, 7, substitute( atop(ex1, ex2), list(ex1=ex1,ex2=ex2)))
> >
> > #and this works
> > text(2, 6, expression(atop(1,2)))
> >
> > I tried to use eval when calling atop, but it did not work either.
> Therefore some hint in help page could be quite handy.
> >
> > Best regards
> > Petr Pikal
> >
> > S pozdravem | Best Regards
> > RNDr. Petr PIKAL
> > Vedoucí Výzkumu a vývoje | Research Manager
> > PRECHEZA a.s.
> > nábř. Dr. Edvarda Beneše 1170/24 | 750 02 Přerov | Czech Republic
> > Tel: +420 581 252 256 | GSM: +420 724 008 364
> > petr.pikal using precheza.cz | www.precheza.cz
> >
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> >
> > -----Original Message-----
> > From: David Winsemius <dwinsemius using comcast.net>
> > Sent: Thursday, April 7, 2022 12:04 AM
> > To: PIKAL Petr <petr.pikal using precheza.cz>; Richard M. Heiberger <
> rmh using temple.edu>
> > Cc: r-help using r-project.org
> > Subject: Re: [R] [External] add equation and rsqared to plot
> >
> >
> > On 4/6/22 14:36, PIKAL Petr wrote:
> > > Hallo David
> > >
> > > Thanks for your answer. atop itself somehow cannot use expression made
> by substitute  although those expressions itself are correct. I asked this
> question after roughly two hours of unsuccessful atempts.
> > >
> > > The second substitute or bquote solves the problem. Maybe this could
> propagate to help page, because although atop works smoothly with simple
> expressions, expressions with substitute are treated in a wrong way (at
> least by my opinion).
> >
> >
> > It's not a problem with `atop`. It's a problem with your understanding
> of how R expressions and plotmath functions work. The argument(s) to
> `expression` are not evaluated. So `atop` was given two expressions `eq`
> and `req` and they in turn were not evaluated .... just taken as text
> values inside atop. Using either `substitute` (with a second argument
> > list) or bquote (with its special dot function) forces evaluation by
> getting from the R symbol table those expressions which you had assigned as
> values of the symbols `eq` and `req`.
> >
> > The plotmath functions (not just atop but also `paste`, `frac`, `over`
> and all the rest on the ?plotmath pafge),  are designed to be "like"
> > `expression` in not evaluating their arguments unless a "special value"
> > like a Greek letter name or a defined %<op>% is found. Those functions
> are handled with a different parser than regular R functions. So they are
> not designed to go out to the R symbol table (which is where even locally
> defined object names are kept) to find values.
> >
> >
> > Hope this helps;
> >
> > David.
> >
> >
> > --
> >
> > David.
> >
> > >
> > > Thanks again.
> > >
> > > Best regards.
> > > Petr
> > >
> > >
> > > ________________________________________
> > > Od: David Winsemius <dwinsemius using comcast.net>
> > > Odesláno: 6. dubna 2022 23:20
> > > Komu: PIKAL Petr; Richard M. Heiberger
> > > Kopie: r-help using r-project.org
> > > Předmět: Re: [R] [External] add equation and rsqared to plot
> > >
> > > Try this:
> > >
> > >
> > > lm_eqn = function(m) {
> > >       l <- list(a = format(coef(m)[1], digits = 4),
> > >                 b = format(abs(coef(m)[2]), digits = 4),
> > >                 r2 = format(summary(m)$r.squared, digits = 3),
> > >                 r2adj = format(summary(m)$adj.r.squared, digits = 3));
> > >       if (coef(m)[2] >= 0)  {
> > >           eq <- substitute(italic(y) == a + b %.% italic(x), l)
> > >       } else {
> > >           eq <- substitute(italic(y) == a - b %.% italic(x),l)
> > >
> > >       }
> > >       req <- substitute(italic(r)^2~"="~r2*
> ","~~italic(adj.r)^2~"="~r2adj,l)
> > >       a_regs <- substitute( atop(eq, req), list(eq=eq,req=req)) }
> > >
> > > --
> > >
> > > David.
> > >
> > > On 4/6/22 13:47, PIKAL Petr wrote:
> > >> Hallo Richard.
> > >>
> > >> Did you try the example? I Used atop but with the syntax I made, the
> > >> result is
> > >>
> > >> eq
> > >> req
> > >>
> > >> but not the equations.
> > >>
> > >> I send the picture, but I am not sure if it will go through.
> > >>
> > >> Best regards
> > >> Petr
> > >>
> > >> ________________________________________
> > >> Od: Richard M. Heiberger <rmh using temple.edu>
> > >> Odesláno: 6. dubna 2022 22:36
> > >> Komu: PIKAL Petr
> > >> Kopie: r-help using r-project.org
> > >> Předmět: Re: [External] [R] add equation and rsqared to plot
> > >>
> > >> I think you are looking for atop(a,b) See ? plotmath
> > >>
> > >>> On Apr 06, 2022, at 15:58, PIKAL Petr <petr.pikal using precheza.cz>
> wrote:
> > >>>
> > >>> Dear all
> > >>>
> > >>>
> > >>> I want to add equation and rsquared values to plot and I am lost in
> correct expression form. I want to have 2 lines, one with equation and one
> with r squared values.
> > >>>
> > >>>
> > >>> Here is what I made.
> > >>>
> > >>> # function to extract values from lm fit.
> > >>>
> > >>>
> > >>> lm_eqn = function(m) {
> > >>>    l <- list(a = format(coef(m)[1], digits = 4),
> > >>>        b = format(abs(coef(m)[2]), digits = 4),
> > >>>        r2 = format(summary(m)$r.squared, digits = 3),
> > >>>        r2adj = format(summary(m)$adj.r.squared, digits = 3));
> > >>>    if (coef(m)[2] >= 0)  {
> > >>>      eq <- substitute(italic(y) == a + b %.% italic(x), l)
> > >>>    } else {
> > >>>      eq <- substitute(italic(y) == a - b %.% italic(x),l)
> > >>>
> > >>>    }
> > >>>    req <- substitute(italic(r)^2~"="~r2*
> ","~~italic(adj.r)^2~"="~r2adj,l)
> > >>>    expression(atop(eq, req))
> > >>> }
> > >>>
> > >>>
> > >>> #Example
> > >>>
> > >>> x <- 1:10
> > >>> y <- x*5 +rnorm(10)
> > >>> plot(x,y)
> > >>> fit <- lm(y~x)
> > >>> text(4,40, lm_eqn(fit))
> > >>>
> > >>>
> > >>> I know that both eq and req are correct expressions and when the
> last line in function is either eq or req, the example gives correct result.
> > >>>
> > >>>
> > >>> But how to get both expressions one above the other is mystery.
> > >>>
> > >>> Please help.
> > >>>
> > >>>
> > >>> Best regards.
> > >>>
> > >>> Petr
> > >>>
> > >>>
> > >>>
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> > >>>
> > >>> ______________________________________________
> > >>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
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> > >>> PLEASE do read the posting guide
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> > >> Osobní údaje: Informace o zpracování a ochraně osobních údajů
> > >> obchodních partnerů PRECHEZA a.s. jsou zveřejněny na:
> > >> https://www.precheza.cz/zasady-ochrany-osobnich-udaju/ | Information
> > >> about processing and protection of business partner’s personal data
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> > >> důvěrné a podléhají tomuto právně závaznému prohláąení o vyloučení
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> > >>
> > >>
> > >> ______________________________________________
> > >> 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.
> > ______________________________________________
> > 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.
>
> ______________________________________________
> 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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