Why is ggplot annotation created with expression and bquote in bold font?

Question

Using ggplot2 I need a multi-line annotation that incorporates variable values, commas, a Greek letter, and a superscript. I played with a lot of different ideas I found in this forum for doing this but nothing I tried worked the way I wanted. I finally adopted a "brute force" method shown in the example code below. The last line of the three-line annotation uses bquote (to include a variable value) and plotmath to add the variable units. The annotation text is fine, but it appears in bold font which is different from the first two lines. I've tried adding "fontface = 'plain'" to all three annotate statements but that doesn't change anything. Is there a way to fix this? I do not want to make all three lines bold. Thanks.

annot_test <- function(){
  require(ggplot2)
  #
  #  Create some data
  #
  x <- c(1:10)
  y <- c(1:10)
  #
  #  Variables to appear in annotation
  #
  day1 <- 201
  dayn <- 210
  station <- c("SU13","SU03","SU05")
  thisYrMn <- 4950
  #
  #  Assemble the text for the annotations
  #
  line1   <- paste("Days: ",day1,"-",dayn,sep="")
  line2   <- paste("Stations: ",
                   station[1],", ",
                   station[2],", ",
                   station[3],sep="")
  line3   <- bquote(paste("Mean: ", .(thisYrMn), 
                          " (",{mu},"g",~m^{-3},")"))
  #
  #  Create the data frame
  #
  df <- data.frame(x,y)
  #
  #  Make a simple plot
  #
  pbase <- ggplot(df, aes(x=x, y=y))
  p1    <- pbase + geom_point()
  
  p1 <- p1 + annotate("text",
             label=line1, 
             x=3.0, 
             y=7.5, 
             hjust=0,
             size=4)
  p1 <- p1 + annotate("text",
             label=line2,
             x=3.0,
             y=7.0,
             size=4,
             hjust=0)
    
  p1 <- p1 + annotate("text",
             label=line3,
             x=3.0,
             y=6.5,
             size=4,
             hjust=0)
  
  print(p1)
}

Enclose the `bquote` call in `deparse()` and pass `parse = TRUE` to the third `annotate` call. That seems to fix the typeface issue and is consistent with the examples in `?annotate` that use `plotmath` syntax. — Mikael Jagan, Jan 24 '22 at 05:40
See also [this](https://stackoverflow.com/questions/50671934) related (duplicate?) question. — Mikael Jagan, Jan 24 '22 at 05:56
Thank you, Mikael. I just tried making those changes but now am getting an error - "Error in parse(text = text[[i]]) : :2:0: unexpected end of input 1: paste("Mean: ", 4950, "(", { " Perhaps I didn't do the dparse wrapping correctly. Does having operating on a pasted string complicate things? — Fleetboat, Jan 24 '22 at 15:05
My mistake. If you are using R version 4.0.0 or higher, then wrap the `bquote` call in `deparse1()`, not `deparse`. If not, then do `paste(deparse(bquote(...)), collapse = " ")`. — Mikael Jagan, Jan 24 '22 at 15:27
No - you were correct (see answer posted below). The problem was with the syntax of the expression. Thank you again. — Fleetboat, Jan 24 '22 at 15:29

score 0 · Answer 1 · edited Jan 24 '22 at 15:37

Thanks to Mikael Jagan's comment, and following up on the error I was getting, the answer is indeed to wrap the bquote call in deparse and use parse = TRUE in the annotate call. The error was caused by the { symbol I was using to offset the mu in the plotmath expression. The corrected code uses:

line3   <- deparse(bquote(paste("Mean: ", .(thisYrMn), 
                          " (",mu,"g",~m^-3,")")))

Why is ggplot annotation created with expression and bquote in bold font?

1 Answers1