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

David Winsemius dw|n@em|u@ @end|ng |rom comc@@t@net
Wed Apr 6 23:25:23 CEST 2022

```On 4/6/22 13:58, Richard M. Heiberger wrote:
> this isn't your example, but it works:
>
> text(5,40, expression(atop(x^2, 3*pi)))
>
> So it looks like your eq and req aren't used at all.  the character strings in your atop statement are used as is.
> You will need bquote() or somethiing similar for what you are attempting.

My earlier answer used `substitute`, but I tested this as the final line
of the function and got success as well:

bquote( atop(.(eq), .(req)))

--

David.

> See the section
>   ## How to combine "math" and numeric variables :
> in the example for plotmath.
>
> Rich
>
>> 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),
>>   if (coef(m)[2] >= 0)  {
>>     eq <- substitute(italic(y) == a + b %.% italic(x), l)
>>   } else {
>>     eq <- substitute(italic(y) == a - b %.% italic(x),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.
>>
>>
>>
>> Best regards.
>>
>> Petr
>>
>>
>>
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