The latest version of ggtern, 1.0.1.0, has several bug-fixes and improvements. One worth mentioning, is the creation of some new geometries to assist in the plotting of constant value lines, analogous to hline and vline in ggplot2.

For Lines of constant T value:

ggtern() + geom_Tline(Tintercept = 0.5, size = 2, color = "red")

For Lines of constant L value:

ggtern() + geom_Lline(Lintercept = 0.5, size = 2, color = "green")

For Lines of constant R value:

ggtern() + geom_Rline(Rintercept = 0.5, size = 2, color = "blue")

Or using some convenience functions that have been included:

ggtern() + 
  Tline(0.5, color = "red", size = 2) + 
  Lline(0.5, color = "green",size = 2) + 
  Rline(0.5, color = "blue", size = 2)

Of course, just like hline and vline in ggplot2, multiple values can be provided

ggtern() + Tline(seq(0.1, 0.9, by = 0.1), color = "red", size = 2)

And they can be used from aesthetic mappings:

df <- data.frame(x = runif(10), y = runif(10), z = runif(10))
df <- df/apply(df, 1, sum)
ggtern() + geom_Lline(data = df, aes(Lintercept = y), color = "green", size = 2)

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