How to add boxplots to scatterplot with jitter

Here's one way using base graphics.

boxplot(NUMS ~ GRP, data = ddf, lwd = 2, ylab = 'NUMS')
stripchart(NUMS ~ GRP, vertical = TRUE, data = ddf, 
    method = "jitter", add = TRUE, pch = 20, col = 'blue')

To do this in ggplot2, try:

ggplot(ddf, aes(x=GRP, y=NUMS)) + 
  geom_boxplot(outlier.shape=NA) + #avoid plotting outliers twice
  geom_jitter(position=position_jitter(width=.1, height=0))

Obviously you can adjust the width and height arguments of position_jitter() to your liking (although I'd recommend height=0 since height jittering will make your plot inaccurate).