Dot plot
Description
In a dot plot, the width of a dot corresponds to the bin width (or maximum width, depending on the binning algorithm), and dots are stacked, with each dot representing one observation.
Usage
1 2 3 4 5 6  geom_dotplot(mapping = NULL, data = NULL, position = "identity", ...,
binwidth = NULL, binaxis = "x", method = "dotdensity",
binpositions = "bygroup", stackdir = "up", stackratio = 1,
dotsize = 1, stackgroups = FALSE, origin = NULL, right = TRUE,
width = 0.9, drop = FALSE, na.rm = FALSE, show.legend = NA,
inherit.aes = TRUE)

Arguments
mapping 
Set of aesthetic mappings created by 
data 
The data to be displayed in this layer. There are three options: If A A 
position 
Position adjustment, either as a string, or the result of a call to a position adjustment function. 
... 
other arguments passed on to 
binwidth 
When 
binaxis 
The axis to bin along, "x" (default) or "y" 
method 
"dotdensity" (default) for dotdensity binning, or "histodot" for fixed bin widths (like stat_bin) 
binpositions 
When 
stackdir 
which direction to stack the dots. "up" (default), "down", "center", "centerwhole" (centered, but with dots aligned) 
stackratio 
how close to stack the dots. Default is 1, where dots just just touch. Use smaller values for closer, overlapping dots. 
dotsize 
The diameter of the dots relative to 
stackgroups 
should dots be stacked across groups? This has the effect
that 
origin 
When 
right 
When 
width 
When 
drop 
If TRUE, remove all bins with zero counts 
na.rm 
If 
show.legend 
logical. Should this layer be included in the legends?

inherit.aes 
If 
Details
There are two basic approaches: dotdensity and histodot.
With dotdensity binning, the bin positions are determined by the data and
binwidth
, which is the maximum width of each bin. See Wilkinson
(1999) for details on the dotdensity binning algorithm. With histodot
binning, the bins have fixed positions and fixed widths, much like a
histogram.
When binning along the x axis and stacking along the y axis, the numbers on y axis are not meaningful, due to technical limitations of ggplot2. You can hide the y axis, as in one of the examples, or manually scale it to match the number of dots.
Aesthetics
\aestheticsgeomdotplot
Computed variables
 x
center of each bin, if binaxis is "x"
 y
center of each bin, if binaxis is "x"
 binwidth
max width of each bin if method is "dotdensity"; width of each bin if method is "histodot"
 count
number of points in bin
 ncount
count, scaled to maximum of 1
 density
density of points in bin, scaled to integrate to 1, if method is "histodot"
 ndensity
density, scaled to maximum of 1, if method is "histodot"
References
Wilkinson, L. (1999) Dot plots. The American Statistician, 53(3), 276281.
Examples
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50  ggplot(mtcars, aes(x = mpg)) + geom_dotplot()
ggplot(mtcars, aes(x = mpg)) + geom_dotplot(binwidth = 1.5)
# Use fixedwidth bins
ggplot(mtcars, aes(x = mpg)) +
geom_dotplot(method="histodot", binwidth = 1.5)
# Some other stacking methods
ggplot(mtcars, aes(x = mpg)) +
geom_dotplot(binwidth = 1.5, stackdir = "center")
ggplot(mtcars, aes(x = mpg)) +
geom_dotplot(binwidth = 1.5, stackdir = "centerwhole")
# y axis isn't really meaningful, so hide it
ggplot(mtcars, aes(x = mpg)) + geom_dotplot(binwidth = 1.5) +
scale_y_continuous(NULL, breaks = NULL)
# Overlap dots vertically
ggplot(mtcars, aes(x = mpg)) + geom_dotplot(binwidth = 1.5, stackratio = .7)
# Expand dot diameter
ggplot(mtcars, aes(x = mpg)) + geom_dotplot(binwidth = 1.5, dotsize = 1.25)
# Examples with stacking along y axis instead of x
ggplot(mtcars, aes(x = 1, y = mpg)) +
geom_dotplot(binaxis = "y", stackdir = "center")
ggplot(mtcars, aes(x = factor(cyl), y = mpg)) +
geom_dotplot(binaxis = "y", stackdir = "center")
ggplot(mtcars, aes(x = factor(cyl), y = mpg)) +
geom_dotplot(binaxis = "y", stackdir = "centerwhole")
ggplot(mtcars, aes(x = factor(vs), fill = factor(cyl), y = mpg)) +
geom_dotplot(binaxis = "y", stackdir = "center", position = "dodge")
# binpositions="all" ensures that the bins are aligned between groups
ggplot(mtcars, aes(x = factor(am), y = mpg)) +
geom_dotplot(binaxis = "y", stackdir = "center", binpositions="all")
# Stacking multiple groups, with different fill
ggplot(mtcars, aes(x = mpg, fill = factor(cyl))) +
geom_dotplot(stackgroups = TRUE, binwidth = 1, binpositions = "all")
ggplot(mtcars, aes(x = mpg, fill = factor(cyl))) +
geom_dotplot(stackgroups = TRUE, binwidth = 1, method = "histodot")
ggplot(mtcars, aes(x = 1, y = mpg, fill = factor(cyl))) +
geom_dotplot(binaxis = "y", stackgroups = TRUE, binwidth = 1, method = "histodot")
