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

[Ben Bolker]

   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]]
> 
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-- 
Dr. Benjamin Bolker
Professor, Mathematics & Statistics and Biology, McMaster University
Director, School of Computational Science and Engineering
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