How to italicize part (one or two words) of an axis title

问题

Is there any way to change the style of part of an axis title while keep the rest part unchanged? In my case, How could I italicize
"bacteria X" in the y-axis title? To my knowledge, the command theme(axis.title.y=element_text(face="italic")) can only change the whole y-aixs title, is it?

ggplot(fig1,aes(x=cf,y=Freq,fill=Var1)) +
geom_bar(stat="identity") +
labs(x="Groups",y="No. of bacteria X isolates with corresponding types",fill="Var1") +
theme(axis.title.y=element_text(face="italic"))

回答1:

You could make an expression like this:

my_y_title <- expression(paste("No. of ", italic("bacteria X"), " isolates with corresponding types"))
.... + labs(y=my_y_title)

回答2:

I believe RFelber's suggestion is what you are after. Try this:

labs(x="Groups",
     y=expression('No. of'~italic(bacteria X)~'isolates with corresponding types'),
     fill="Var1")

I did not need to use the bquote() function. The tildes produce single spaces for terms that are outside of the quotes.

来源：https://stackoverflow.com/questions/32555531/how-to-italicize-part-one-or-two-words-of-an-axis-title