geom_boxplot. ggplot2 0.9.2.1

Usage

geom_boxplot(mapping = NULL, data = NULL, stat = "boxplot", position = "dodge", outlier.colour = "black",
  outlier.shape = 16, outlier.size = 2, notch = FALSE, notchwidth = 0.5, ...)

Arguments

outlier.colour: colour for outlying points
outlier.shape: shape of outlying points
outlier.size: size of outlying points
notch: if FALSE (default) make a standard box plot. If TRUE, make a notched box plot. Notches are used to compare groups; if the notches of two boxes do not overlap, this is strong evidence that the medians differ.
notchwidth: for a notched box plot, width of the notch relative to the body (default 0.5)
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 overlappling points on this layer
...: other arguments passed on to layer. This can include aesthetics whose values you want to set, not map. See layer for more details.

Description

The upper and lower "hinges" correspond to the first and third quartiles (the 25th and 75th percentiles). This differs slightly from the method used by the boxplot function, and may be apparent with small samples. See boxplot.stats for for more information on how hinge positions are calculated for boxplot.

Details

The upper whisker extends from the hinge to the highest value that is within 1.5 * IQR of the hinge, where IQR is the inter-quartile range, or distance between the first and third quartiles. The lower whisker extends from the hinge to the lowest value within 1.5 * IQR of the hinge. Data beyond the end of the whiskers are outliers and plotted as points (as specified by Tukey).

In a notched box plot, the notches extend 1.58 * IQR / sqrt(n). This gives a roughly 95 interval for comparing medians. See McGill et al. (1978) for more details.

Aesthetics

geom_boxplot understands the following aesthetics (required aesthetics are in bold):

lower
middle
upper
x
ymax
ymin
alpha
colour
fill
linetype
shape
size
weight

References

McGill, R., Tukey, J. W. and Larsen, W. A. (1978) Variations of box plots. The American Statistician 32, 12-16.

Examples


p <- ggplot(mtcars, aes(factor(cyl), mpg))

p + geom_boxplot()

qplot(factor(cyl), mpg, data = mtcars, geom = "boxplot")


p + geom_boxplot() + geom_jitter()

p + geom_boxplot() + coord_flip()

qplot(factor(cyl), mpg, data = mtcars, geom = "boxplot") +
  coord_flip()


p + geom_boxplot(notch = TRUE)
Warning message:
notch went outside hinges. Try setting notch=FALSE.
Warning message:
notch went outside hinges. Try setting notch=FALSE.

p + geom_boxplot(notch = TRUE, notchwidth = .3)
Warning message:
notch went outside hinges. Try setting notch=FALSE.
Warning message:
notch went outside hinges. Try setting notch=FALSE.


p + geom_boxplot(outlier.colour = "green", outlier.size = 3)


# Add aesthetic mappings
# Note that boxplots are automatically dodged when any aesthetic is
# a factor
p + geom_boxplot(aes(fill = cyl))

p + geom_boxplot(aes(fill = factor(cyl)))

p + geom_boxplot(aes(fill = factor(vs)))

p + geom_boxplot(aes(fill = factor(am)))


# Set aesthetics to fixed value
p + geom_boxplot(fill = "grey80", colour = "#3366FF")

qplot(factor(cyl), mpg, data = mtcars, geom = "boxplot",
  colour = I("#3366FF"))


# Scales vs. coordinate transforms -------
# Scale transformations occur before the boxplot statistics are computed.
# Coordinate transformations occur afterwards.  Observe the effect on the
# number of outliers.
library(plyr) # to access round_any
m <- ggplot(movies, aes(y = votes, x = rating,
   group = round_any(rating, 0.5)))
m + geom_boxplot()
Warning message:
position_dodge requires constant width: output may be incorrect

m + geom_boxplot() + scale_y_log10()
Warning message:
position_dodge requires constant width: output may be incorrect

m + geom_boxplot() + coord_trans(y = "log10")
Warning message:
position_dodge requires constant width: output may be incorrect

m + geom_boxplot() + scale_y_log10() + coord_trans(y = "log10")
Warning message:
position_dodge requires constant width: output may be incorrect


# Boxplots with continuous x:
# Use the group aesthetic to group observations in boxplots
qplot(year, budget, data = movies, geom = "boxplot")
Warning message:
Removed 53573 rows containing non-finite values (stat_boxplot).

qplot(year, budget, data = movies, geom = "boxplot",
  group = round_any(year, 10, floor))
Warning message:
Removed 53573 rows containing non-finite values (stat_boxplot).
Warning message:
position_dodge requires constant width: output may be incorrect


# Using precomputed statistics
# generate sample data
abc <- adply(matrix(rnorm(100), ncol = 5), 2, quantile, c(0, .25, .5, .75, 1))
b <- ggplot(abc, aes(x = X1, ymin = `0%`, lower = `25%`, middle = `50%`, upper = `75%`, ymax = `100%`))
b + geom_boxplot(stat = "identity")

b + geom_boxplot(stat = "identity") + coord_flip()

b + geom_boxplot(aes(fill = X1), stat = "identity")

Box and whiskers plot.