ggplot transparency on individual bar

Question

I am currently attempting to use ggplot to create a bar chart with a single bar that is partially transparent.

I have the following code:

dt1 <- data         


        

Answer 1

First you put the alpha inside the aes as suggested by @jazzurro. However, you should use factor for this to get a discrete scale. Then you can manually adjust the alpha scale.

ggplot() + geom_bar(data=dt1, aes(x=yr, y=val, fill=x, alpha=factor(alphayr)), stat="identity") +
  scale_x_continuous(breaks=dt1$yr) +
  scale_alpha_manual(values = c("0.5"=0.5, "1"=1), guide='none')