labeller: Generic labeller function for facets

 p1 <- ggplot(mtcars, aes(x = mpg, y = wt)) + geom_point()  # You can assign different labellers to variables: p1 + facet_grid(vs + am ~ gear,  labeller = labeller(vs = label_both, am = label_value))  # Or whole margins: p1 + facet_grid(vs + am ~ gear,  labeller = labeller(.rows = label_both, .cols = label_value))  # You can supply functions operating on strings: capitalize <- function(string) {  substr(string, 1, 1) <- toupper(substr(string, 1, 1))  string } p2 <- ggplot(msleep, aes(x = sleep_total, y = awake)) + geom_point() p2 + facet_grid(vore ~ conservation, labeller = labeller(vore = capitalize))  # Or use character vectors as lookup tables: conservation_status <- c(  cd = "Conservation Dependent",  en = "Endangered",  lc = "Least concern",  nt = "Near Threatened",  vu = "Vulnerable",  domesticated = "Domesticated" ) ## Source: http://en.wikipedia.org/wiki/Wikipedia:Conservation_status  p2 + facet_grid(vore ~ conservation, labeller = labeller(  .default = capitalize,  conservation = conservation_status ))  # In the following example, we rename the levels to the long form, # then apply a wrap labeller to the columns to prevent cropped text msleep$conservation2 <- plyr::revalue(msleep$conservation,  conservation_status)  p2 %+% msleep + facet_grid(vore ~ conservation2) p2 %+% msleep +  facet_grid(vore ~ conservation2,  labeller = labeller(conservation2 = label_wrap_gen(10))  )  # labeller() is especially useful to act as a global labeller. You # can set it up once and use it on a range of different plots with # different facet specifications.  global_labeller <- labeller(  vore = capitalize,  conservation = conservation_status,  conservation2 = label_wrap_gen(10),  .default = label_both )  p2 + facet_grid(vore ~ conservation, labeller = global_labeller) p2 + facet_wrap(~vore, labeller = global_labeller) p2 %+% msleep + facet_wrap(~conservation2, labeller = global_labeller)