Change the shape of ALL outliers in jittered boxplot

Question

I've looked around the net and found lots of stuff about jittering and changing the shape of outliers but can't seem to find anything about this specific problem.

I want a black and white boxplot with jittered data points - I can do that.

I would also like to change the shape of outliers. Although there are multiple cases with a score of 4 only one of them changes to a hollow circle.

I would assume that if one data point at a particular level is considered an outlier the rest would be considered outliers too.

Is this a coding error or did I miss something along the way in a stats class? If it's a coding thing how do I get all of them to be hollow?

Apparently my "reputation" needs to be 10 to get attach an image! I hope it makes sense without it though

Here's my code:

plot <- ggplot(phase2.3, aes(Group, Score))

plot + geom_point (position = position_jitter(w = 0.1, h = 0.2)) + 
 geom_boxplot (outlier.shape = 1) + xlab("Group") + theme_bw(20)

Answer 1

You probably have to calculate, which points are outside the range by yourself. Here is an extension of the standard example from geom_boxplot that shows how to find the outliers using plyr.

# load packages
require(plyr)
require(ggplot2)
# find outliers
df <- ddply(mtcars, "cyl", function(x){
  iqr <- quantile(x[,"mpg"], c(.25, .75)) # inter-quartile-range
  whisker <- iqr+c(-1.5, 1.5)*diff(iqr)   # whiskers-range
  x[,"shape"] <- ifelse(x[,"mpg"] < whisker[1] | x[,"mpg"]>whisker[2], 1, 16)
  return(x)
})
# plot
p <- ggplot(df, aes(factor(cyl), mpg))
p + geom_boxplot() # without jittering
# adding shape manualy
p + geom_boxplot(outlier.size=-Inf) + 
  geom_jitter(aes(shape=factor(shape))) + 
  scale_shape_manual(guide=FALSE, values=c("16"=16, "1"=1))