Bagaimana cara mengubah label facet?

Saya telah menggunakan ggplotperintah berikut : ggplot(survey, aes(x = age)) + stat_bin(aes(n = nrow(h3), y = ..count.. / n), binwidth = 10) + scale_y_continuous(formatter = "percent", breaks = c(0, 0.1, 0.2)) + facet_grid(hospital ~ .) + theme(panel.background = theme_blank()) untuk...