bquote does not work in facet_grid labels in ggplot2 version 2.1

Question

I have the following code that worked perfectly in some old pre-2.1 version of ggplot2:

dd <-
structure(list(Dataset = structure(c(1L, 1L, 1L, 1L, 1L, 1L), .Label = c("train", 
"validation"), class = "factor"), Iterations = c(4L, 2L, 3L, 
4L, 1L, 3L), L1 = c(1e-07, 1e-07, 1e-07, 1e-06, 1e-07, 1e-06), 
    L2 = c(1e-05, 1e-05, 1e-05, 1e-05, 1e-05, 1e-05), Accuracy = c(0.2079478, 
    0.2079829, 0.2081201, 0.2086698, 0.2091378, 0.2093453), Loss = c(0.4468469, 
    0.446877, 0.4472973, 0.4485992, 0.4496757, 0.4499354)), .Names = c("Dataset", 
"Iterations", "L1", "L2", "Accuracy", "Loss"), row.names = c(NA, 
6L), class = "data.frame")

labelAxis <- function(i) {
  function(values) {
    sapply(values, function(x) { bquote(lambda[.(i)]==10^.(round(log10(x)))) })
  }
}

ggplot(dd, aes(x=Iterations, y=Loss, color=Dataset)) +
  facet_grid(. ~ L1 + L2, scales="fixed",
             labeller=labeller(L1=labelAxis(1), L2=labelAxis(2), keep.as.numeric=T)) +
  geom_line()

Now ggplot2 deprecates the labeller() keep.as.numeric=... parameter, and, worse yet, for the code above it no longer produces nice math rendering of the labels. Does anyone know how to fix that issue?

Answer 1

Ok, I think I've figured it out. The new way to edit facet labels is to use label_bquote(), like this:

ggplot(dd, aes(x=Iterations, y=Loss, color=Dataset)) +
  facet_grid(. ~ L1 + L2, scales="fixed", labeller=label_bquote(
    cols={lambda[1]==10^.(round(log10(L1)))}*", "*lambda[2]==10^.(round(log10(L2))))) +
  geom_line()

Note that seemingly random pair of curly braces. That's an R gotcha. Without those braces R parser chokes on a second == operator in the expression.