[R] Is it odd or not? about I() function

[Hiroto Miyoshi]

Dear R experts,

Thank you all for your help.
Now, I know that the ggplot is causing the issue and that
setting the y=as.numeric(rslt_with_I) can fix the problem,
that should suffice for now, since I am not an R expert.

In addition, this time, I could learn that there is a class
of "AsIs", and that the ggplot might not expect the use
of "AsIs" class in the data.  This is a bit of learning for me.

Thank you, again.  Your responses helped me a lot.
Sincerely,

Hiroto


On 2025/04/21 6:24, peter dalgaard wrote:
> What Ben says. Also a bit of pragmatic advice:
>
> If you want people to help you and run your scripts, don't precede each line with 9 characters that they'll have to remove to make it runnable. (Emacs users can do "C-x r k", but there aren't that many Emacs users around these days.)
>
> Also, the script is overly complicated and expects the user to (install and) load a bunch of stuff, where the effect that you are talking about is just as clearly visible in simpler code like this.
>
> ggplot(dta, aes(x = x, y = as.numeric(y)))+geom_line()
> x <- 1:10; y <- rnorm(10) ; dta <- data.frame(x,y)
> ggplot(dta, aes(x = x, y = y )) + geom_line()
> ggplot(dta, aes(x = x, y = I(y) )) + geom_line()
>
> However, like Ben, I'm not quite up to drilling into the ggplot code to see where things go wrong.
>
> Apparently, you can leave out the geom_line() bit and still get the odd y scale, so the issue is inside ggplot() it self and perhaps you could do something like debug(ggplot2:::ggplot_build.ggplot) and single-step and see if you can spot where and how the y scale is being set up.
>
> -pd
>
>
>> On 19 Apr 2025, at 23.15, Ben Bolker <bbolker using gmail.com> wrote:
>>
>>   This is obviously not a complete answer, but if you look at the data closely:
>>
>> str(dta)
>> 'data.frame': 40 obs. of  6 variables:
>> $ x             : num  0.915 0.937 0.286 0.83 0.642 ...
>> $ y             : num  0.3796 0.4358 0.0374 0.9735 0.4318 ...
>> $ z             : int  1 1 1 1 1 1 1 1 1 1 ...
>> $ x_axis        : int  1 2 3 4 5 6 7 8 9 10 ...
>> $ rslt_without_I: num  0.7657 0.8474 0.0516 1.1533 0.483 ...
>> $ rslt_with_I   : 'AsIs' num  0.765658.... 0.847406.... 0.051648.... 1.153295.... 0.482993.... ...
>>
>> you'll see that the two variables have different *classes*. Your '==' test checks to see if the *numeric values* of the elements are the same.
>>
>> Both of these, which check the characteristics of the vector itself as well as the values of the elements, indicate that these vectors are indeed different.
>>
>> identical(dta$rslt_with_I, dta$rslt_without_I)
>> all.equal(dta$rslt_with_I, dta$rslt_without_I)
>>
>>   In order to figure out *why* having class "AsIs" rather than class "numeric" makes the axis/breaks computation fail, you'd have to dig into the machinery (or, ask on the ggplot issues list -- the questions there involving "AsIs" mostly refer to a separate use case for "AsIs" ... https://github.com/tidyverse/ggplot2/issues?q=is%3Aissue%20AsIs )
>>
>>
>> On 2025-04-18 9:46 p.m., Hiroto Miyoshi wrote:
>>> Dear R expert
>>> I encountered a bewildering situation, about which
>>> I am seeking help.  I wrote a following toy script
>>> which can recreate the situation.
>>> --- the script begins here ---
>>>      1   │ library(tidyverse)
>>>      2   │ library(rlist)
>>>      3   │ library(patchwork)
>>>      4   │ set.seed(42)
>>>      5   │ f <- function(x, y, z, x_axis) {
>>>      6   │   rslt_with_I <- I(x^2 * 0.5) + I(x * y)
>>>      7   │   rslt_without_I <- (x^2 * 0.5) + (x * y)
>>>      8   │   out <- data.frame(rslt_without_I, rslt_with_I)
>>>      9   │   return(out)
>>>     10   │ }
>>>     11   │
>>>     12   │ df <- data.frame(
>>>     13   │   x = runif(40, 0, 1),
>>>     14   │   y = runif(40, 0, 1),
>>>     15   │   z = rep(1:4, rep(10, 4)),
>>>     16   │   x_axis = rep(1:10, 4)
>>>     17   │ )
>>>     18   │
>>>     19   │ dta <- pmap(df, f) %>%
>>>     20   │   list.stack(.) %>%
>>>     21   │   cbind(df, .)
>>>     22   │
>>>     23   │ g1 <- ggplot(dta, aes(x = x_axis, y = rslt_with_I, color =
>>> factor(z))) +
>>>     24   │   geom_point() +
>>>     25   │   geom_line()
>>>     26   │ g2 <- ggplot(dta, aes(x = x_axis, y = rslt_without_I, color =
>>> factor(z))) +
>>>     27   │   geom_point() +
>>>     28   │   geom_line()
>>>     29   │
>>>     30   │ g <- g1 | g2
>>>     31   │ plot(g)
>>>     32   │
>>>     33   │ dta$rslt_with_I == dta$rslt_without_I
>>>     34   │ # the end of the script
>>> The two graphs, i.e. g1 and g2 are different and obviously, the data do not
>>> fit in the graph area for g1. The command "dta$rslt_with_I ==
>>> dta$rslt_without_I"
>>> shows the plotted data are identical.  I want why this happens.
>>> Sincerely
>>> Hiroto
>>> [[alternative HTML version deleted]]
>>> ______________________________________________
>>> 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.
>> -- 
>> Dr. Benjamin Bolker
>> Professor, Mathematics & Statistics and Biology, McMaster University
>> Director, School of Computational Science and Engineering
>>> E-mail is sent at my convenience; I don't expect replies outside of working hours.
>> ______________________________________________
>> 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.