Include formatted subscript in mtext?

问题

Admittedly I am new to R but I have looked around quite a bit and I can't seem to solve this.

For superscript this works lovely

mtext(expression(paste( italic("h") ^ italic("2"))), side=2, line = 2, cex=cexm) 

but when I try to get a subscript using the same approach

mtext(expression(paste(italic("I") [] italic("a"))),side=2, line=2,cex=cexm)

or

mtext(expression(paste(italic("I"), italic(["a"]))),side=2, line=2,cex=cexm)

plus several other variations on this theme

R keeps telling me that there is an unexpected [

Any help would be greatly appreciated, apologies if this is addressed elsewhere but I did not succeed in finding it.

回答1:

In the first instance the paste call is entirely superfluous since the argument is a valid R expression:

 mtext(expression( italic("h") ^ italic("2")), side=2, line = 2) # works

In the second instance paste is also unnecessary:

 mtext(expression( italic("I") [italic("a")] ),side=2, line=2,cex=cexm)

The argument to the plotmath-"[" function needs to be inside the paired "[]"-symbols.

来源：https://stackoverflow.com/questions/28664385/include-formatted-subscript-in-mtext