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

Thu Apr 7 00:03:58 CEST 2022

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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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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