Using "expression" to create list of labels with some italics, using values from a datafra-CodePudding

I'm trying to create a list of labels that contain italics. I can do it with "expression" like this, and when I put them on a plot (by adding a legend as an example, but I'll use them different ways), it all works nicely.

sp.names=c(expression(paste("species ",italic("one")," sp.")),
           expression(paste("species ",italic("two")," sp.")))
plot(1:10)
legend("topleft",legend=sp.names)

But instead of specifying the words in the label directly in the code, I want to call them from cells in a dataframe (because there are a lot of them and they change depending on my underlying data). But when I try and specify which dataframe cell I want, it doesn't print the labels correctly (see below). Perhaps there is a different way for me to call the cell that I want that the "expression" function will recognise?

df=data.frame(V1=c("species","species","species"),V2=c("one","two","three"))
sp.names=c(expression(paste(df$V1[1],italic(df$V2[1])," sp.")),
           expression(paste(df$V1[2],italic(df$V2[2])," sp.")))
plot(1:10)
legend("topleft",legend=sp.names)

CodePudding user response：

Use substitute, it substitutes variables in expressions.

sp.names=c(substitute(V1 ~ italic(V2) ~ "sp.", df[1,]),
           substitute(V1 ~ italic(V2) ~ "sp.", df[2,]))

I also removed the unneeded paste (which has a different meaning within plotmath) and replaced it with ~ for increased readability.

CodePudding user response：

Give bquote a shot.

sp.names <- c(bquote(.(df$V1[1])~italic(.(df$V2[1]))~" sp."),
              bquote(.(df$V1[2])~italic(.(df$V2[2]))~" sp."))

plot(1:10)
legend("topleft", legend=sp.names)