Why ggtern doesn't plots some points?

Question

I'm trying to do a plot from a data.frame that contains positive and negative values and I cannot plot all points. Someone know, if is possible to adapt the code to plot all point?

example = data.frame(X1=c(-1,-0.5,1),X2=c(-1,0.7,1),X3=c(1,-0.5,2))
ggtern(data=example, aes(x=X1,y=X2,z=X3)) + geom_point()

Answer 1

Well actually your points are getting plotted, but they lie outside the plot region.

Firstly, to understand why, each row of your data must sum to unity, else it will be coerced that way, therefore what you will be plotting is the following:

example = example / matrix(rep(rowSums(example),ncol(example)),nrow(example),ncol(example))
example

        X1        X2        X3
1 1.000000  1.000000 -1.000000
2 1.666667 -2.333333  1.666667
3 0.250000  0.250000  0.500000

Now the rows sum to unity:

print(rowSums(example))
[1] 1 1 1

You have negative values, which are nonsensical in terms of 'composition', however, negative concentrations can still be plotted, as they will numerically represent points outside the ternary area, lets expand the limits and render to see where they lie:

ggtern(data=example, aes(x=X1,y=X2,z=X3)) + 
  geom_mask() + 
  geom_point() +
  limit_tern(5,5,5)