geom_dotplot: 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

geom_dotplot(mapping = NULL, data = NULL, stat = "bindot",
  position = "identity", na.rm = FALSE, binwidth = NULL, binaxis = "x",
  method = "dotdensity", binpositions = "bygroup", stackdir = "up",
  stackratio = 1, dotsize = 1, stackgroups = FALSE, ...)

Arguments

mapping

The aesthetic mapping, usually constructed with aes or aes_string. Only needs to be set at the layer level if you are overriding the plot defaults.

data

A layer specific dataset - only needed if you want to override the plot defaults.

stat

The statistical transformation to use on the data for this layer.

position

The position adjustment to use for overlapping points on this layer

na.rm

If FALSE (the default), removes missing values with a warning. If TRUE silently removes missing values.

binwidth

When method is "dotdensity", this specifies maximum bin width. When method is "histodot", this specifies bin width. Defaults to 1/30 of the range of the data

binaxis

which axis to bin along "x" (default) or "y"

method

"dotdensity" (default) for dot-density binning, or "histodot" for fixed bin widths (like stat_bin)

binpositions

When method is "dotdensity", "bygroup" (default) determines positions of the bins for each group separately. "all" determines positions of the bins with all the data taken together; this is used for aligning dot stacks across multiple groups.

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 binwidth, default 1.

stackgroups

should dots be stacked across groups? This has the effect that position = "stack" should have, but can't (because this geom has some odd properties).

...

other arguments passed on to layer. This can include aesthetics whose values you want to set, not map. See layer for more details.

Aesthetics

[results=rd,stage=build]{ggplot2:::rd_aesthetics("geom", "dotplot")} ggplot(mtcars, aes(x = mpg)) + geom_dotplot() ggplot(mtcars, aes(x = mpg)) + geom_dotplot(binwidth = 1.5)

# Use fixed-width 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(name = "", 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")

# Use qplot instead qplot(mpg, data = mtcars, geom = "dotplot")

Wilkinson, L. (1999) Dot plots. The American Statistician, 53(3), 276-281.

Details

With dot-density 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 dot-density 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.