Modifying the decimal mark of stat_poly_eq

Question

I use the stat_poly_eq function from the ggpmisc package to add the regression equation in my ggplots. It works perfectly. However, I'd like to change the decimal mark of the equation from period to comma, and I can't figure out how to do this. Any suggestions?

data(mpg)

ggplot(mpg, aes(y = displ, x = hwy)) +
  geom_point(alpha = 0.5, color = "cadetblue") +
  geom_smooth(method = "lm", se = F, color = "black", size = 0.5) +
  stat_poly_eq(aes(label = paste(after_stat(eq.label),
                                 after_stat(rr.label),
                                 sep = "*plain(\",\")~~")),
               coef.digits = 3)

It works for the equation, but not for the R-squared... I also would like an alternative that would not change my global options... — Fernanda Peres, Dec 15 '22 at 14:34
Well, you can always `oldopts = options(...) ; ggplot(...) ... ; options(oldopts)`. But it *is* weird that it does not work for the `R²`. — January, Dec 15 '22 at 14:45
Just for completeness. This was a bug in recent versions of 'ggpmisc'. It is now fixed in 'ggpmisc' 0.5.2 now in CRAN. — Pedro J. Aphalo, Dec 19 '22 at 23:09

score 2 · Answer 1 · answered Dec 15 '22 at 15:01

2

data(mpg)
library(ggpmisc)

my_formula <- y ~ x
myformat <- "y = %s %s x, R²: %s"

ggplot(mpg, aes(y = displ, x = hwy)) +
  geom_point(alpha = 0.5, color = "cadetblue") +
  geom_smooth(method = "lm", se = F, color = "black", size = 0.5) +
  stat_poly_eq(
    formula = my_formula, output.type = "numeric",
    mapping = aes(
      label = 
        sprintf(
          myformat,
          format(stat(coef.ls)[[1]][[1, "Estimate"]], digits = 3, decimal.mark = ","),
          format(stat(coef.ls)[[1]][[2, "Estimate"]], digits = 2, decimal.mark = ","),
          format(stat(r.squared), digits = 2, decimal.mark = ",")))
  )

I have elaborated my answer based on this post.

I hope this helps you!

answered Dec 15 '22 at 15:01

Esther

356
8

You're welcome, I'm glad to hear it! – Esther Dec 15 '22 at 15:33
This is a bug. Next version of 'ggpmisc' will obey the "OutDec" R option. I should have thought of this! (I am a native Spanish speaker...) – Pedro J. Aphalo Dec 15 '22 at 23:43
It seems that there is not clean way to fix this: https://stackoverflow.com/questions/23586741/change-decimal-character-in-sprintf I will most likely have to add to the package the `gsub()` kludge. The root of the problem is that 'ggpmisc' code makes use of `sprintf()`, while `sprintf()` uses the operating system's locale setting. – Pedro J. Aphalo Dec 16 '22 at 14:42

score 1 · Accepted Answer · answered Dec 15 '22 at 15:04

You can simply swap the periods for commas using gsub in the rr.label. The eq.label is parsed as an expression, so the period needs to be replaced with something like *paste(',')* for this to work:

ggplot(mpg, aes(y = displ, x = hwy)) +
  geom_point(alpha = 0.5, color = "cadetblue") +
  geom_smooth(method = "lm", se = F, color = "black", size = 0.5) +
  stat_poly_eq(aes(label = paste(gsub('\\.', "*paste(',')*", 
                                      after_stat(eq.label)),
                                 gsub('\\.', ",", after_stat(rr.label)),
                                 sep = "*plain(\",\")~~")),
               coef.digits = 3, size = 6)

Great! I had tried gsub but without success. Your suggestion works perfectly! Thank you! — Fernanda Peres, Dec 15 '22 at 15:32

Pedro J. Aphalo · Answer 3 · 2022-12-19T23:14:52.683

'ggpmsic' 0.5.2 is now in CRAN. Bug fixed (I hope) Important: because of the way 'ggplot2' works the option must be set to the desired decimal marker when the plots is rendered (printer or exported to a graphical format). (The option as set when the gg object is created or saved to a variable does not affect the object itself.)

library(ggpmisc) # version >= 0.5.2
#> Loading required package: ggpp
#> Loading required package: ggplot2
#> 
#> Attaching package: 'ggpp'
#> The following object is masked from 'package:ggplot2':
#> 
#>     annotate

old.option <- options(OutDec = ",")

ggplot(mpg, aes(y = displ, x = hwy)) +
  geom_point(alpha = 0.5, color = "cadetblue") +
  geom_smooth(method = "lm", se = F, color = "black", linewidth = 0.5) +
  stat_poly_eq(aes(label = paste(after_stat(eq.label),
                                 after_stat(rr.label),
                                 sep = "*plain(\";\")~~")),
               coef.digits = 3)
#> `geom_smooth()` using formula = 'y ~ x'

options(old.option)

I also replaced size with linewidth to avoid a warning from 'ggplot2' 3.4.0, and changed the comma in sep to a semicolon as it seems better when the decimal mark is a comma.

^{Created on 2022-12-20 with reprex v2.0.2}

Modifying the decimal mark of stat_poly_eq

3 Answers3