The boxplot compactly displays the distribution of a continuous variable. It visualises five summary statistics (the median, two hinges and two whiskers), and all "outlying" points individually.
geom_boxplot(mapping = NULL, data = NULL, stat = "boxplot", position = "dodge", ..., outlier.colour = NULL, outlier.color = NULL, outlier.fill = NULL, outlier.shape = 19, outlier.size = 1.5, outlier.stroke = 0.5, outlier.alpha = NULL, notch = FALSE, notchwidth = 0.5, varwidth = FALSE, na.rm = FALSE, show.legend = NA, inherit.aes = TRUE) stat_boxplot(mapping = NULL, data = NULL, geom = "boxplot", position = "dodge", ..., coef = 1.5, na.rm = FALSE, show.legend = NA, inherit.aes = TRUE)
Set of aesthetic mappings created by
aes_. If specified and
inherit.aes = TRUE (the
default), it is combined with the default mapping at the top level of the
plot. You must supply
mapping if there is no plot mapping.
The data to be displayed in this layer. There are three options:
NULL, the default, the data is inherited from the plot
data as specified in the call to
data.frame, or other object, will override the plot
data. All objects will be fortified to produce a data frame. See
fortify for which variables will be created.
function will be called with a single argument,
the plot data. The return value must be a
will be used as the layer data.
Position adjustment, either as a string, or the result of a call to a position adjustment function.
other arguments passed on to
layer. These are
often aesthetics, used to set an aesthetic to a fixed value, like
color = "red" or
size = 3. They may also be parameters
to the paired geom/stat.
Default aesthetics for outliers. Set to
NULL to inherit from the
aesthetics used for the box.
In the unlikely event you specify both US and UK spellings of colour, the US spelling will take precedence.
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 suggests that the medians
are significantly different.
for a notched box plot, width of the notch relative to the body (default 0.5)
FALSE (default) make a standard box plot. If
TRUE, boxes are drawn with widths proportional to the
square-roots of the number of observations in the groups (possibly
weighted, using the
FALSE, the default, missing values are removed with
a warning. If
TRUE, missing values are silently removed.
logical. Should this layer be included in the legends?
NA, the default, includes if any aesthetics are mapped.
FALSE never includes, and
TRUE always includes.
FALSE, overrides the default aesthetics,
rather than combining with them. This is most useful for helper functions
that define both data and aesthetics and shouldn't inherit behaviour from
the default plot specification, e.g.
Use to override the default connection between
length of the whiskers as multiple of IQR. Defaults to 1.5
The lower and upper hinges correspond to the first and third quartiles
(the 25th and 75th percentiles). This differs slightly from the method used
boxplot function, and may be apparent with small samples.
boxplot.stats for for more information on how hinge
positions are calculated for
The upper whisker extends from the hinge to the largest value no further than 1.5 * IQR from 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 smallest value at most 1.5 * IQR of the hinge. Data beyond the end of the whiskers are called "outlying" points and are plotted individually.
In a notched box plot, the notches extend
1.58 * IQR / sqrt(n).
This gives a roughly 95% confidence interval for comparing medians.
See McGill et al. (1978) for more details.
geom_boxplot understands the following aesthetics (required aesthetics are in bold):
width of boxplot
lower whisker = smallest observation greater than or equal to lower hinge - 1.5 * IQR
lower hinge, 25% quantile
lower edge of notch = median - 1.58 * IQR / sqrt(n)
median, 50% quantile
upper edge of notch = median + 1.58 * IQR / sqrt(n)
upper hinge, 75% quantile
upper whisker = largest observation less than or equal to upper hinge + 1.5 * IQR
McGill, R., Tukey, J. W. and Larsen, W. A. (1978) Variations of box plots. The American Statistician 32, 12-16.
p + geom_boxplot() + geom_jitter(width = 0.2)p + geom_boxplot() + coord_flip()p + geom_boxplot(notch = TRUE)#>#>p + geom_boxplot(varwidth = TRUE)p + geom_boxplot(fill = "white", colour = "#3366FF")# By default, outlier points match the colour of the box. Use # outlier.colour to override p + geom_boxplot(outlier.colour = "red", outlier.shape = 1)# Boxplots are automatically dodged when any aesthetic is a factor p + geom_boxplot(aes(colour = drv))# You can also use boxplots with continuous x, as long as you supply # a grouping variable. cut_width is particularly useful ggplot(diamonds, aes(carat, price)) + geom_boxplot()#> Warning: Continuous x aesthetic -- did you forget aes(group=...)?ggplot(diamonds, aes(carat, price)) + geom_boxplot(aes(group = cut_width(carat, 0.25)), outlier.alpha = 0.1)# It's possible to draw a boxplot with your own computations if you # use stat = "identity": y <- rnorm(100) df <- data.frame( x = 1, y0 = min(y), y25 = quantile(y, 0.25), y50 = median(y), y75 = quantile(y, 0.75), y100 = max(y) ) ggplot(df, aes(x)) + geom_boxplot( aes(ymin = y0, lower = y25, middle = y50, upper = y75, ymax = y100), stat = "identity" )