Using italic() with a variable in ggplot2 title expression

Question

When I make a map using ggplot2 and attempt to italicize part of the figure title using a combination of expression() and italic() using a string, my map comes out as desired:

plottitle <- expression(paste('Example map with ', italic('italics')))

crimes <- data.frame(state = tolower(rownames(USArrests)), USArrests)
states_map <- map_data("state")
map <- ggplot(crimes, aes(map_id = state)) + 
  geom_map(aes(fill = Murder), 
           map = states_map) + 
  expand_limits(x = states_map$long, 
                y = states_map$lat) +
  labs(title = plottitle)

map

However, when I try to do the same thing, but use an object instead of a string, the object does not evaluate to the desired string:

word <- 'italics'
plottitle2 <- expression(paste('Example map with ', italic(word)))

map <- ggplot(crimes, aes(map_id = state)) + 
  geom_map(aes(fill = Murder), 
           map = states_map) + 
  expand_limits(x = states_map$long, 
                y = states_map$lat) +
  labs(title = plottitle2)

map

How can I get the vector word to evaluate before applying italic()?

score 13 · Accepted Answer · answered Aug 10 '15 at 19:57

13

bquote or substitute should work,

 a = 'text' 
 plot(1,1, main=bquote(italic(.(a))))
 plot(1,1, main=substitute(italic(x), list(x=a)))

answered Aug 10 '15 at 19:57

baptiste

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Thanks for the answer -- could you please translate this to my example above? I'm trying to paste together `word` and "Example map with " – mcjudd Aug 10 '15 at 20:02
2

`bquote('Example map with'~italic(.(word)))` – baptiste Aug 10 '15 at 20:46
2

or `substitute('Example map with'~italic(x), list(x=word))` – baptiste Aug 10 '15 at 20:48

Using italic() with a variable in ggplot2 title expression

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