How to use Greek symbols in ggplot2?

Question

My categories need to be named with Greek letters. I am using ggplot2, and it works beautifully with the data. Unfortunately I cannot figure out how to put those greek symbols on the x axis (at the tick marks) and also make them appear in the legend. Is there any way to do it?

UPDATE: I had a look at the link, however, there is no good method described to accomplish what I want to do.

Emilieemiline

See the discussion of the expression function here: https://mcmap.net/q/103868/-getting-latex-into-r-plots – Four

Is there any hint on obtaining the viewports from a ggplot2. If that can be done, I believe that changing x-tic marks will be straight forward. – Emilieemiline

You can use latex2exp package: cran.r-project.org/web/packages/latex2exp/vignettes/… – Ozoniferous

Answer 1

Here is a link to an excellent wiki that explains how to put greek symbols in ggplot2. In summary, here is what you do to obtain greek symbols

1. Text Labels: Use parse = T inside geom_text or annotate.
2. Axis Labels: Use expression(alpha) to get greek alpha.
3. Facet Labels: Use labeller = label_parsed inside facet.
4. Legend Labels: Use bquote(alpha == .(value)) in legend label.

You can see detailed usage of these options in the link

EDIT. The objective of using greek symbols along the tick marks can be achieved as follows

require(ggplot2);
data(tips);
p0 = qplot(sex, data = tips, geom = 'bar');
p1 = p0 + scale_x_discrete(labels = c('Female' = expression(alpha),
                                      'Male'   = expression(beta)));
print(p1);

For complete documentation on the various symbols that are available when doing this and how to use them, see ?plotmath.

Hutt

I want those Greek Symbols to mark the tics. I am not sure I follow this answer. I will try this and write back. Thank you for the direction. – Emilieemiline

This doesnt work for my purpose at least. Thank you for the pointer though. – Emilieemiline

@Sam, check out the example code in my edit. It gives you greek symbols along your x-axis tick marks. Is this what you were looking for? – Hutt

I would like to add an asterisk ('*') after a Greek letter. Anyone know how to do this? – Valois

I recently learned that another option is to use substitute, this also works in places where expression does not work, and even allows other formatting like italics, bold etc. – Emilieemiline

This is now out of date for legend labels. See ?scales::label_parse() – Bollinger

Answer 2

Simplest solution: Use Unicode Characters

No expression or other packages needed.
Not sure if this is a newer feature for ggplot, but it works. It also makes it easy to mix Greek and regular text (like adding '*' to the ticks)

Just use unicode characters within the text string. seems to work well for all options I can think of. Edit: previously it did not work in facet labels. This has apparently been fixed at some point.

library(ggplot2)
ggplot(mtcars, 
       aes(mpg, disp, color=factor(gear))) + 
  geom_point() + 
  labs(title="Title (\u03b1 \u03a9)", # works fine
       x= "\u03b1 \u03a9 x-axis title",    # works fine
       y= "\u03b1 \u03a9 y-axis title",    # works fine
       color="\u03b1 \u03a9 Groups:") +  # works fine
  scale_x_continuous(breaks = seq(10, 35, 5), 
                     labels = paste0(seq(10, 35, 5), "\u03a9*")) + # works fine; to label the ticks
  ggrepel::geom_text_repel(aes(label = paste(rownames(mtcars), "\u03a9*")), size =3) + # works fine 
  facet_grid(~paste0(gear, " Gears \u03a9"))

^{Created on 2019-08-28 by the reprex package (v0.3.0)}

Decontaminate

Nice answer. For more on unicode characters, see: #27691229 – Re

very flexible!! – Stevenson

This is the best way because you don't faff about with the object types formed by expression or bquote - you end up with a character object that you can use in any other way you use character objects. – Fortuneteller

This is not only the easiest Method, but also the best, since it works in most cases and doesn't rely on other functions. – Hindenburg

This generates a lot of warnings, about a hundred lines of: Warning message in grid.Call(C_textBounds, as.graphicsAnnot(x$label), x$x, x$y, : “conversion failure on '>3σ' in 'mbcsToSbcs': dot substituted for <cf> – Laliberte

Sorry @Patafikss, I cannot reproduce any error messages. I would guess it may be a system issue. you may try it wit omitting the ggrepel line which introduces another package. – Decontaminate

I solved the issue. I needed to use device = cairo_pdf in the ggsave(). Using Linux here, it's apparently a problem of the default device. – Laliberte

Answer 3

Use expression(delta) where 'delta' for lowercase δ and 'Delta' to get capital Δ.

Here's full list of Greek characters:

Α α alpha
Β β beta
Γ γ gamma
Δ δ delta
Ε ε epsilon
Ζ ζ zeta
Η η eta
Θ θ theta
Ι ι iota
Κ κ kappa
Λ λ lambda
Μ μ mu
Ν ν nu
Ξ ξ xi
Ο ο omicron
Π π pi
Ρ ρ rho
Σ σ sigma
Τ τ tau
Υ υ upsilon
Φ φ phi
Χ χ chi
Ψ ψ psi
Ω ω omega

EDIT: Copied from comments, when using in conjunction with other words use like: expression(Delta*"price")

Sosthena

How can I get a label like Δprice? expression(Deltaprice) doesn't work, neither does expression(Delta price) – Entebbe

thanks. But how's that exactly? xlab(expression(Delta)price) gives an error – Entebbe

expression(Delta*price) – Neiman

Is there a way to get a Greek-form (as opposed to Latin-form) Upsilon? See en.wikipedia.org/wiki/Upsilon Correspondence with Latin Y (I'd like something like the third character in en.wikipedia.org/wiki/Upsilon#/media/…) – Impassive

expression(Delta*"price") works. Don't love the syntax. – Grouper

Answer 4

You do not need the latex2exp package to do what you wanted to do. The following code would do the trick.

ggplot(smr, aes(Fuel.Rate, Eng.Speed.Ave., color=Eng.Speed.Max.)) + 
  geom_point() + 
  labs(title=expression("Fuel Efficiency"~(alpha*Omega)), 
color=expression(alpha*Omega), x=expression(Delta~price))

Also, some comments (unanswered as of this point) asked about putting an asterisk (*) after a Greek letter. expression(alpha~"*") works, so I suggest giving it a try.

More comments asked about getting Δ Price and I find the most straightforward way to achieve that is expression(Delta~price)). If you need to add something before the Greek letter, you can also do this: expression(Indicative~Delta~price) which gets you:

Selwin