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

[Hiroto Miyoshi]

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
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