Capital Greek Letters in ggplot legends

[Rodrigo Plei]

Dear all,

I am working on a heatmap using ggplot2, and I need to put the greek letter "omega" in capital form in the legend.

I tried several google searches and modified my script accordingly without success.

Here my script (adapted from a public domain script took from R-bloggers:

#------

ggheatmap2 <- ggplot(AHM, aes(Var1, Var2, fill = value))+

  geom_tile(color = "white")+

  scale_fill_gradient2(low = "white", high = "blue4", mid = "white", 

                       space = "Lab", 

                       name="Grand Mean") +

  #theme_minimal()+ # minimal theme

  theme(legend.title = element_text(size = 12),legend.text=element_text(size=12))+

  theme(axis.text.x = element_text(angle = 360, vjust = 1, 

                                   size = 12, hjust = 1))+

  theme(axis.text.y = element_text(angle = 360, vjust = 1, 

                                   size = 12, hjust = 1))+

  coord_fixed()

# Print the heatmap

print(ggheatmap2)

#------

Where "AHM" is my dataset.

I tried several arguments to put the capital omega using the argument "name" as above, but all failed.

I would greatly appreciate any help.

Happy new year,

Rodrigo

[Sherif Soliman]

Hi Rodrigo,

Did you come across this page?
http://www.cookbook-r.com/Graphs/Legends_(ggplot2)/

See the "Modifying the text of legend titles and labels" heading.

We don't have your data so I can't try to reproduce your exact plot, but here is an example using the built-in iris dataset:

ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width)) +
    geom_point(aes(color = Species)) +
    scale_color_discrete(name="Ω")

As you can see, the trick is to use the name argument in scale_color_discrete() or in your case since you're using scall_fill_gradient2 to use scale_fill_discrete() to set the legend title.

Does this do what you need?

Sherif

[Ben Bolker]

For what it's worth I think I'd slightly prefer using the ?plotmath
interface:

g0 <- ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width)) +
geom_point(aes(color = Species))
g0 + scale_colour_discrete(name=~Omega)

The tilde (~) gets ggplot to interpret what follows as an
*expression*, which means it gets handed to the parser used as in
?plotmath; this is more flexible (and probably more robust
cross-platform?), i.e. you could do something like

g0 + scale_colour_discrete(name=~hat(Omega))

If you want to go to the next level of elegance, look into the tikz
package, e.g.
http://iltabiai.github.io/tips/latex/2015/09/15/latex-tikzdevice-r.html

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[Sherif Soliman]

On 3 Jan 2017, at 16:08, Ben Bolker wrote:

> For what it's worth I think I'd slightly prefer using the ?plotmath
> interface:
>
> g0 <- ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width)) +
> geom_point(aes(color = Species))
> g0 + scale_colour_discrete(name=~Omega)
>
> The tilde (~) gets ggplot to interpret what follows as an
> *expression*, which means it gets handed to the parser used as in
> ?plotmath; this is more flexible (and probably more robust
> cross-platform?), i.e. you could do something like
>
> g0 + scale_colour_discrete(name=~hat(Omega))
>
> If you want to go to the next level of elegance, look into the tikz
> package, e.g.
> http://iltabiai.github.io/tips/latex/2015/09/15/latex-tikzdevice-r.html
>
>

That's very cool. I had no idea this ability/interface existed.

It does produce a different looking "Omega" though - a
characteristically LaTeX-looking one. Still, very cool, thanks for
sharing.

Sherif

[Brian]

Hi Rodrigo,
please check out ?plotmath to supply the correct "expression".

From the hip:

name = expression(Omega)

HTH,
Brian