Using paste() and formatC() together in plot label in R

Question

I want to use a subscript and a number in a geom_text() layer of a ggplot2 plot. The number will come from an indexed dataframe so that I can use it in a flexible way within a custom function, but here is a simpler reproducible example:

temp_line <- structure(list(x = c(670.892544634835, 670.94367492675, 670.994805218665, 
671.04593551058, 671.097065802495, 671.14819609441, 671.199326386325, 
671.25045667824, 671.301586970155, 671.35271726207, 671.403847553985, 
671.4549778459, 671.506108137815, 671.55723842973, 671.608368721645, 
671.65949901356, 671.710629305475, 671.76175959739, 671.812889889305, 
671.86402018122, 671.915150473135, 671.96628076505, 672.017411056965, 
672.06854134888, 672.119671640795, 672.17080193271, 672.221932224625, 
672.27306251654, 672.324192808455, 672.37532310037, 672.426453392285, 
672.4775836842, 672.528713976115, 672.57984426803, 672.630974559945, 
672.68210485186), y = c(0.985240554809607, 0.982213133032921, 
0.986693753084667, 0.987366974516756, 0.987636649598203, 0.982056033377924, 
0.980484643703154, 0.983029322815495, 0.988833379596215, 0.983723421126925, 
0.984861430761356, 0.975375941059582, 0.973793277004997, 0.974896425651856, 
0.976215113076567, 0.980190883847887, 0.97234555785344, 0.976564419204803, 
0.971411825270084, 0.958092987035761, 0.948933680537213, 0.944433555718954, 
0.955207036644352, 0.966236032356096, 0.97461001903587, 0.982502838158965, 
0.977806030386617, 0.980102357820749, 0.971970360584438, 0.972510182292617, 
0.971868273995148, 0.986332867356837, 0.992939055558675, 1, 0.990384208442822, 
0.987140151281311)), class = "data.frame", row.names = c(NA, 
-36L))

temp <- structure(list(x = 671.96628076505, y = 0.943555524955473), class = "data.frame", row.names = "window_mins")

temp_num <- c(window_mins = 0.000878030763480352)


# Attempt at plotting equation using paste()
  ggplot() +
    geom_line(data = temp_line, 
              aes(x = x, y = y), alpha = 0.85, size = 0.6) +
    geom_point(data = temp,
               aes(x = x, y = y), alpha = 0.85, size = 1.5, shape = 15) +
    geom_text(data = temp,
              aes(x = x, y = y),
              label = paste("L1 - L[tot] = ", 
                                       formatC(temp_num, 
                                               format = "e", digits = 3)),
              nudge_x = -0.45,
              show.legend = FALSE)

The challenge is using paste() in a way that works for both the subscript and the formatted number. I tried using expression() and paste() together. This creates the correct subscript, but unfortunately prints the command and arguments for formatC() instead of evaluating to produce the number:

label = expression(paste("L1 - ", L[tot], "= ", 
                                       formatC(temp_num, 
                                               format = "e", digits = 3)))

I tried the above but wrapping the formatC command in eval() but I couldn't get that to work. I also played around with wrapping the whole expression in parse() and substitute() based on the links below. What am I missing to generate both a subscript and a formatted number within a paste() command?

Related posts I looked at: Combining paste() and expression() functions in plot labels

https://community.rstudio.com/t/use-bquote-in-ggplot2-for-subscript-text/40882

R - how to combine expression(), paste() and formatC() commands for one legend element?

Use bquote. I'm not sure if you are aware that paste within plotmath expressions is not the usual paste function. — Roland
– Roland, Commented May 26, 2021 at 16:58

Roland · Accepted Answer · 2021-05-27 06:11:27Z

OK, this was surprisingly tricky.

First of all, you need to study help("plotmath"). Then, I would pass a character string and let ggplot2 parse it. If we do that, the RHS of the equation should be specified as a character string, otherwise standard print formatting will be applied within plotmath. I prefer sprintf for convenience but if you insist you can construct the same character string with a combination of paste and formatC.

#note the single quotes within the string
sprintf("L1 - L[tot] == '%.3e'", temp_num)
#[1] "L1 - L[tot] == '8.780e-04'"

ggplot() +
  geom_line(data = temp_line, 
            aes(x = x, y = y), alpha = 0.85, size = 0.6) +
  geom_point(data = temp,
             aes(x = x, y = y), alpha = 0.85, size = 1.5, shape = 15) +
  geom_text(data = temp,
            aes(x = x, y = y),
            label = sprintf("L1 - L[tot] == '%.3e'", temp_num),
            nudge_x = -0.45,
            show.legend = FALSE,
            parse = TRUE)

Collectives™ on Stack Overflow

Using paste() and formatC() together in plot label in R

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related