nf2 <- mutate(nf, wd = wday(date, label = TRUE))
nf2 <- mutate(nf2, wd = factor(wd))
nf2 <- mutate(nf2, mw = factor(monthweek(day, wday(date))))
nf2 <- mutate(nf2, mw = factor(mw, rev(levels(mw))))
            
ggplot(nf2, aes(x = wd, y = mw, fill = n)) +
    geom_tile(color = "white") +
    scale_fill_gradient(low = "white") +
    facet_wrap(~ month(date, TRUE)) +
    ylab("") + xlab("Week of Month") +
    theme(panel.grid.major = element_blank(),
          axis.text.x = element_text(angle = 45, hjust = 1))