Multiple plots by factor in ggplot (facets)

Question

I have a data frame with two qualitative variables (Q1, Q2) which are both measured on a scale of LOW, MEDIUM, HIGH and a continuous variable CV on a scale 0-100.

s = 5
trial <- data.frame(id = c(1:s), 
                Q1 = ordered(sample(c("LOW","MED","HIGH"),size=s,replace=T)), 
                Q2 = ordered(sample(c("LOW","MED","HIGH"),size=s,replace=T)), 
                CV = runif(s,0,100))

I need to use ggplot to show a faceted plot (preferably a horizontal boxplot/jitter) of the continous variable for each qualitative variable (x2) for each level (x3). This would result in a 3 x 2 layout.

As I'm very new to ggplot I'm unsure how this should be achieved. I've played with qplot and and can't work out how to control the facets to display both Q1 and Q2 boxplots on the same chart!!

Do I need to run multiple qplots to the same window (in base I would use par to control layout) or can it be achieved from a single command. Or should I try to melt the data twice?

trial = rbind(data.frame(Q = "Q1",Level = trial[,2], CV = trial[,4]),
          data.frame(Q = "Q2",Level = trial[,3], CV = trial[,4]))

I'll keep trying and hope somebody can provide some hints in the meantime.

Matthew Plourde Matthew Plourde · Accepted Answer · 2012-06-11T20:59:11

I'm not entirely clear on what you want, but maybe this helps:

ggplot(trial, aes(Level, CV)) + 
   geom_boxplot() + 
   geom_jitter() + 
   facet_wrap(~Q) + 
   coord_flip()

Multiple plots by factor in ggplot (facets)

1 Answers