make paired, inverted histograms

Question

I would like to make paired dotplot histograms for two groups across a set of different tests with the two groups shown in opposite directions on the y-axis. Using this simple data set ``` dat <- data.frame(score = rnorm(100), group = rep(c("Control", "Experimental"), 50), test = rep(LETTERS[1:2], each=50)) ``` I can make faceted dotplots like this ``` ggplot(dat, aes(score, fill=group)) + facet_wrap(~ test) + geom_dotplot(binwidth = 1, dotsize = 1) ``` but I want the Control dots to be pointing down rather than up. Using this question and answer, I can make a histogram version that looks more or less like what I want ``` ggplot() + geom_histogram(data=subset(dat, group=="Experimental"), aes(score, fill="Experimental", y= ..count..)) + geom_histogram(data=subset(dat, group=="Control"), aes(score, fill="Control", y= -..count..)) + scale_fill_hue("Group") ``` but now the faceting is gone. I know I could do the faceting manually using `grid.arrange`, but that would be laborious (my actua…

Accepted Answer

A careful reading of `geom_dotplot` will pay dividends:

```
ggplot() +
  facet_wrap(~test) +
  geom_dotplot(data=subset(dat, group=="Experimental"), aes(score, fill="Experimental")) +
  geom_dotplot(data=subset(dat, group=="Control"), aes(score, fill="Control"),stackdir = "down") +
  scale_fill_hue("Group")
```

I didn't know of the `stackdir` argument off the top of my head. I had to look it up!

make paired, inverted histograms

Solution

Problem