# boxplot

##### Box Plots

Produce box-and-whisker plot(s) of the given (grouped) values.

- Keywords
- hplot

##### Usage

`boxplot(x, …)`# S3 method for formula
boxplot(formula, data = NULL, …, subset, na.action = NULL,
drop = FALSE, sep = ".", lex.order = FALSE)

# S3 method for default
boxplot(x, …, range = 1.5, width = NULL, varwidth = FALSE,
notch = FALSE, outline = TRUE, names, plot = TRUE,
border = par("fg"), col = NULL, log = "",
pars = list(boxwex = 0.8, staplewex = 0.5, outwex = 0.5),
horizontal = FALSE, add = FALSE, at = NULL)

##### Arguments

- formula
a formula, such as

`y ~ grp`

, where`y`

is a numeric vector of data values to be split into groups according to the grouping variable`grp`

(usually a factor).- data
a data.frame (or list) from which the variables in

`formula`

should be taken.- subset
an optional vector specifying a subset of observations to be used for plotting.

- na.action
a function which indicates what should happen when the data contain

`NA`

s. The default is to ignore missing values in either the response or the group.- drop, sep, lex.order
passed to

`split.default`

, see there.- x
for specifying data from which the boxplots are to be produced. Either a numeric vector, or a single list containing such vectors. Additional unnamed arguments specify further data as separate vectors (each corresponding to a component boxplot).

`NA`

s are allowed in the data.- …
For the

`formula`

method, named arguments to be passed to the default method.For the default method, unnamed arguments are additional data vectors (unless

`x`

is a list when they are ignored), and named arguments are arguments and graphical parameters to be passed to`bxp`

in addition to the ones given by argument`pars`

(and override those in`pars`

). Note that`bxp`

may or may not make use of graphical parameters it is passed: see its documentation.- range
this determines how far the plot whiskers extend out from the box. If

`range`

is positive, the whiskers extend to the most extreme data point which is no more than`range`

times the interquartile range from the box. A value of zero causes the whiskers to extend to the data extremes.- width
a vector giving the relative widths of the boxes making up the plot.

- varwidth
if

`varwidth`

is`TRUE`

, the boxes are drawn with widths proportional to the square-roots of the number of observations in the groups.- notch
if

`notch`

is`TRUE`

, a notch is drawn in each side of the boxes. If the notches of two plots do not overlap this is ‘strong evidence’ that the two medians differ (Chambers*et al*, 1983, p.62). See`boxplot.stats`

for the calculations used.- outline
if

`outline`

is not true, the outliers are not drawn (as points whereas S+ uses lines).- names
group labels which will be printed under each boxplot. Can be a character vector or an expression (see plotmath).

- boxwex
a scale factor to be applied to all boxes. When there are only a few groups, the appearance of the plot can be improved by making the boxes narrower.

- staplewex
staple line width expansion, proportional to box width.

- outwex
outlier line width expansion, proportional to box width.

- plot
if

`TRUE`

(the default) then a boxplot is produced. If not, the summaries which the boxplots are based on are returned.- border
an optional vector of colors for the outlines of the boxplots. The values in

`border`

are recycled if the length of`border`

is less than the number of plots.- col
if

`col`

is non-null it is assumed to contain colors to be used to colour the bodies of the box plots. By default they are in the background colour.- log
character indicating if x or y or both coordinates should be plotted in log scale.

- pars
a list of (potentially many) more graphical parameters, e.g.,

`boxwex`

or`outpch`

; these are passed to`bxp`

(if`plot`

is true); for details, see there.- horizontal
logical indicating if the boxplots should be horizontal; default

`FALSE`

means vertical boxes.- add
logical, if true

*add*boxplot to current plot.- at
numeric vector giving the locations where the boxplots should be drawn, particularly when

`add = TRUE`

; defaults to`1:n`

where`n`

is the number of boxes.

##### Details

The generic function `boxplot`

currently has a default method
(`boxplot.default`

) and a formula interface (`boxplot.formula`

).

If multiple groups are supplied either as multiple arguments or via a
formula, parallel boxplots will be plotted, in the order of the
arguments or the order of the levels of the factor (see
`factor`

).

Missing values are ignored when forming boxplots.

##### Value

List with the following components:

a matrix, each column contains the extreme of the lower whisker, the lower hinge, the median, the upper hinge and the extreme of the upper whisker for one group/plot. If all the inputs have the same class attribute, so will this component.

a vector with the number of observations in each group.

a matrix where each column contains the lower and upper extremes of the notch.

the values of any data points which lie beyond the extremes of the whiskers.

a vector of the same length as `out`

whose elements
indicate to which group the outlier belongs.

a vector of names for the groups.

##### References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
*The New S Language*.
Wadsworth & Brooks/Cole.

Chambers, J. M., Cleveland, W. S., Kleiner, B. and Tukey, P. A. (1983)
*Graphical Methods for Data Analysis.* Wadsworth & Brooks/Cole.

Murrell, P. (2005) *R Graphics*. Chapman & Hall/CRC Press.

See also `boxplot.stats`

.

##### See Also

`boxplot.stats`

which does the computation,
`bxp`

for the plotting and more examples;
and `stripchart`

for an alternative (with small data
sets).

##### Examples

`library(graphics)`

```
## boxplot on a formula:
boxplot(count ~ spray, data = InsectSprays, col = "lightgray")
# *add* notches (somewhat funny here):
boxplot(count ~ spray, data = InsectSprays,
notch = TRUE, add = TRUE, col = "blue")
boxplot(decrease ~ treatment, data = OrchardSprays,
log = "y", col = "bisque")
rb <- boxplot(decrease ~ treatment, data = OrchardSprays, col = "bisque")
title("Comparing boxplot()s and non-robust mean +/- SD")
mn.t <- tapply(OrchardSprays$decrease, OrchardSprays$treatment, mean)
sd.t <- tapply(OrchardSprays$decrease, OrchardSprays$treatment, sd)
xi <- 0.3 + seq(rb$n)
points(xi, mn.t, col = "orange", pch = 18)
arrows(xi, mn.t - sd.t, xi, mn.t + sd.t,
code = 3, col = "pink", angle = 75, length = .1)
## boxplot on a matrix:
mat <- cbind(Uni05 = (1:100)/21, Norm = rnorm(100),
`5T` = rt(100, df = 5), Gam2 = rgamma(100, shape = 2))
boxplot(mat) # directly, calling boxplot.matrix()
## boxplot on a data frame:
df. <- as.data.frame(mat)
par(las = 1) # all axis labels horizontal
boxplot(df., main = "boxplot(*, horizontal = TRUE)", horizontal = TRUE)
## Using 'at = ' and adding boxplots -- example idea by Roger Bivand :
boxplot(len ~ dose, data = ToothGrowth,
boxwex = 0.25, at = 1:3 - 0.2,
subset = supp == "VC", col = "yellow",
main = "Guinea Pigs' Tooth Growth",
xlab = "Vitamin C dose mg",
ylab = "tooth length",
xlim = c(0.5, 3.5), ylim = c(0, 35), yaxs = "i")
boxplot(len ~ dose, data = ToothGrowth, add = TRUE,
boxwex = 0.25, at = 1:3 + 0.2,
subset = supp == "OJ", col = "orange")
legend(2, 9, c("Ascorbic acid", "Orange juice"),
fill = c("yellow", "orange"))
## With less effort (slightly different) using factor *interaction*:
boxplot(len ~ dose:supp, data = ToothGrowth,
boxwex = 0.5, col = c("orange", "yellow"),
main = "Guinea Pigs' Tooth Growth",
xlab = "Vitamin C dose mg", ylab = "tooth length",
sep = ":", lex.order = TRUE, ylim = c(0, 35), yaxs = "i")
## more examples in help(bxp)
```

*Documentation reproduced from package graphics, version 3.4.0, License: Part of R 3.4.0*

### Community examples

**mark@niemannross.com**at Oct 5, 2018 graphics v3.5.1

```r boxplot(mtcars$mpg) boxplot(mpg ~ cyl, data = mtcars, col = "lightgray", varwidth = TRUE, main = "mpg vs cylinders", ylab = "mpg",xlab = "cylinders") fivenum(mtcars$mpg) # the numbers used to create the boxplot # video tutorial at http://niemannross.com/link/boxplot ```

**shweyeenwe@gmail.com**at Sep 6, 2017 graphics v3.4.0

**shweyeenwe@gmail.com**at Sep 6, 2017 graphics v3.4.0