R: Complex Axis Format Expression

Question

I am using ggplot2 and trying to incorporate a complex expression using paste and expression altogether.

For example, I am trying to show a value of 0.5e-6 as 0.5 micro second and also (5 x 10^-7 seconds) in the y-axis labels.

So far I am able to do either of this, but not both. A minimal working example is given below.

library(ggplot2)

dat <- data.frame(
  A = factor(c("O", "O", "P", "P", "Q", "Q", "O", "O", "P", "P", "Q", "Q"), levels=c("O", "O", "P", "P", "Q", "Q","O", "O", "P", "P", "Q", "Q")),
  B = factor(c("P-0.1", "P-0.1", "P-0.1", "P-0.1","P-0.1", "P-0.1",  "P-0.2", "P-0.2", "P-0.2", "P-0.2", "P-0.2", "P-0.2"), levels = c("P-0.1", "P-0.1", "P-0.1", "P-0.1","P-0.1", "P-0.1",  "P-0.2", "P-0.2", "P-0.2", "P-0.2", "P-0.2", "P-0.2")),
  X = c( 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1),
  Y = c(1e-6, 1.5e-6, 1.2e-6, 1.3e-6, 0.9e-6, 1.4e-6, 3.0e-6, 2.0e-6, 3.2e-6, 2.1e-6, 2.7e-6, 1.9e-6)
)

fancy_scientific_text <- function(l) {
  # turn in to character string in scientific notation
  l <- format(l, scientific = TRUE)
  # quote the part before the exponent to keep all the digits
  l <- gsub("^(.*)e", "'\\1'e", l)
  l <- gsub("e\\+","e",l)
  # turn the 'e+' into plotmath format
  l <- gsub("e", "%*%10^", l)
  # print (l)
  l <- gsub("\\'1[\\.0]*\\'\\%\\*\\%", "", l)
  l <- gsub("\\'0[\\.0]*\\'\\%\\*\\%10\\^00", "0", l)
  return(l)
}

fancy_scientific <- function(l) {
  # return this as an expression
  parse(text=fancy_scientific_text(l))
}


human_time_format <- function(y){
  if (!is.na(y)){
    substitute(paste(m, " ", mu, "s", sep=""), list(m=y*1e6))
  }
}

human_times <- function(x = NULL, smbl ="sec"){
  sapply(x, human_time_format)
}

human_time_format_combined <- function(y){
  if (!is.na(y)){
    substitute(paste(y_lab, " (", m, " ", mu, "s)", sep=""), list(m=y*1e6, y_lab=fancy_scientific(y)))
  }
}

human_times_combined <- function(x = NULL, smbl ="sec"){
  sapply(x, human_time_format_combined)
}



p = ggplot(data=dat, aes(x=X, y=Y, colour=A, size=A, shape=A, linetype=A, fill=B, group=interaction(A,B))) + geom_point() + geom_line() + theme_bw()
p = p + geom_point(size=4, alpha=0) + geom_point(size=4, show.legend=FALSE) + guides(shape = guide_legend(nrow=3, byrow = TRUE, keywidth = 1.5, keyheight = 1), colour = guide_legend(override.aes = list(alpha=1)))

p = p + scale_shape_manual(name="", values=c(21,22,23))
p = p + scale_colour_manual(name="", values=c("#005ccc", "#007700", "#56B4E9"))
p = p + scale_linetype_manual(name="", values=c(0,0,1))
p = p + scale_size_manual(name="", values = c(1, 1, 1))
p = p + scale_fill_manual(name = "", values = c("red", "blue"), guide = guide_legend(override.aes = list(shape = 22, size = 5)))

p0 = p + ggtitle("p0")
p1 = p + scale_y_continuous(name = "Y", labels = fancy_scientific) + ggtitle("p1")
p2 = p + scale_y_continuous(name = "Y", labels = human_times) + ggtitle("p2")
p3 = p + scale_y_continuous(name = "Y", labels = human_times_combined) + ggtitle("p3")

And here is the output:

p0 is the unformatted version. p1 is a version with scientific format, p2 is a version with metric unit format, and p3 is the intended format which have both p1 and p2's format. But I could not capture the scientific format here.

Please provide a proper [reproducible example](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) with sample input data and simple code we can run to try out possible solutions. Show where you are trying to use these expressions. This will make it much easier to help you. — MrFlick, Mar 15 '17 at 20:59
Maybe you just want `substitute(paste("(", exp_lbl, ")", m, " ", mu, sm, sep = ""), list(m=y*1e6, sm = smbl, exp_lbl=fancy_scientific(y)[[1]]))`. Again, not sure because you didn't provide a way to test. — MrFlick, Mar 15 '17 at 21:02
@MrFlick I wanted a little bit different stuff. I will add a simple example, soon to clarify. I understand that the things I wanted is not clear enough. — max, Mar 15 '17 at 21:06
Hi @MrFlick, I have added a reproducible example. Please have a look. — max, Mar 16 '17 at 03:29

score 1 · Accepted Answer · answered Mar 16 '17 at 14:42

This is basically what I put in the comment. You can't embed an "expression" inside another expression. You need to combine the calls inside the expression. You can get at the contents of the expression via indexing. So if you change the human_time_format_combined function to extract the contents of the expression returned by fancy_scientific, you'll be all set

human_time_format_combined <- function(y){
  if (!is.na(y)){
    substitute(paste(y_lab, " (", m, " ", mu, "s)", sep=""), 
        list(m=y*1e6, y_lab=fancy_scientific(y)[[1]]))
  }
}

Then p3 will return

Also note that you often don't need paste() since it doesn't do exactly what you think it does in the context of ?plotmath expressions. It can often be replaced by *. For example

human_time_format <- function(y){
  if (!is.na(y)){
    substitute(m*mu*"s", list(m=y*1e6))
  }
}

human_time_format_combined <- function(y){
  if (!is.na(y)){
    substitute(y_lab~~(m*" "*mu*"s"), list(m=y*1e6, y_lab=fancy_scientific(y)[[1]]))
  }
}

Thank you very much. This is very enlightening. – max Mar 21 '17 at 20:31 — max, Mar 21 '17 at 20:31

R: Complex Axis Format Expression

1 Answers1