Why pies are flat in geom_scatterpie in R?

Why are the pies flat?

    df<- data.frame(
      Day=(1:6),
      Var1=c(172,186,191,201,205,208),
      Var2= c(109,483,64010,161992,801775,2505264), A=c(10,2,3,4.5,16.5,39.6), B=c(10,3,0,1.4,4.8,11.9), C=c(2,5,2,0.1,0.5,1.2), D=c(0,0,0,0,0.1,0.2))

ggplot() + 
  geom_scatterpie(data = df, aes(x = Var1 , y = Var2, group = Var1), cols = c("A", "B", "C", "D")) 

I have tried using coord_fixed() and does not work either.

The problem seems to be the scales of the x- and y-axes. If you rescaled them to both to have zero mean and unit variance, the plot works. So, one thing you could do is plot the rescaled values, but transform the labels back into the original scale. To do this, you would have to do the following:

Make the data:

df<- data.frame(
    Day=(1:6),
    Var1=c(172,186,191,201,205,208),
    Var2= c(109,483,64010,161992,801775,2505264), A=c(10,2,3,4.5,16.5,39.6), B=c(10,3,0,1.4,4.8,11.9), C=c(2,5,2,0.1,0.5,1.2), D=c(0,0,0,0,0.1,0.2))

Rescale the variables

df <- df %>% 
    mutate(x = c(scale(Var1)), 
           y = c(scale(Var2)))

Find the linear map that transforms the rescaled values back into their original values. Then, you can use the coefficients from the model to make a function that will transform the rescaled values back into the original ones.

m1 <- lm(Var1 ~ x, data=df)
m2 <- lm(Var2 ~ y, data=df)
trans_x <- function(x)round(coef(m1)[1] + coef(m1)[2]*x)
trans_y <- function(x)round(coef(m2)[1] + coef(m2)[2]*x)

Make the plot, using the transformation functions as the call to labels in the scale_[xy]_continuous() functions

ggplot() + 
    geom_scatterpie(data=df, aes(x = x, y=y), cols = c("A", "B", "C", "D")) + 
    scale_x_continuous(labels = trans_x) + 
    scale_y_continuous(labels = trans_y) + 
    coord_fixed() 

There may be an easier way than this, but it wasn't apparent to me.