geom_bar.Rd

% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/geom-bar.r, R/geom-col.r, R/stat-count.r
\name{geom_bar}
\alias{geom_bar}
\alias{geom_col}
\alias{stat_count}
\title{Bar charts}
\usage{
geom_bar(
  mapping = NULL,
  data = NULL,
  stat = "count",
  position = "stack",
  ...,
  width = NULL,
  na.rm = FALSE,
  orientation = NA,
  show.legend = NA,
  inherit.aes = TRUE
)

geom_col(
  mapping = NULL,
  data = NULL,
  position = "stack",
  ...,
  width = NULL,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

stat_count(
  mapping = NULL,
  data = NULL,
  geom = "bar",
  position = "stack",
  ...,
  width = NULL,
  na.rm = FALSE,
  orientation = NA,
  show.legend = NA,
  inherit.aes = TRUE
)
}
\arguments{
\item{mapping}{Set of aesthetic mappings created by \code{\link[=aes]{aes()}} or
\code{\link[=aes_]{aes_()}}. If specified and \code{inherit.aes = TRUE} (the
default), it is combined with the default mapping at the top level of the
plot. You must supply \code{mapping} if there is no plot mapping.}

\item{data}{The data to be displayed in this layer. There are three
options:

If \code{NULL}, the default, the data is inherited from the plot
data as specified in the call to \code{\link[=ggplot]{ggplot()}}.

A \code{data.frame}, or other object, will override the plot
data. All objects will be fortified to produce a data frame. See
\code{\link[=fortify]{fortify()}} for which variables will be created.

A \code{function} will be called with a single argument,
the plot data. The return value must be a \code{data.frame}, and
will be used as the layer data. A \code{function} can be created
from a \code{formula} (e.g. \code{~ head(.x, 10)}).}

\item{position}{Position adjustment, either as a string, or the result of
a call to a position adjustment function.}

\item{...}{Other arguments passed on to \code{\link[=layer]{layer()}}. These are
often aesthetics, used to set an aesthetic to a fixed value, like
\code{colour = "red"} or \code{size = 3}. They may also be parameters
to the paired geom/stat.}

\item{width}{Bar width. By default, set to 90\% of the resolution of the data.}

\item{na.rm}{If \code{FALSE}, the default, missing values are removed with
a warning. If \code{TRUE}, missing values are silently removed.}

\item{orientation}{The orientation of the layer. The default (\code{NA})
automatically determines the orientation from the aesthetic mapping. In the
rare event that this fails it can be given explicitly by setting \code{orientation}
to either \code{"x"} or \code{"y"}. See the \emph{Orientation} section for more detail.}

\item{show.legend}{logical. Should this layer be included in the legends?
\code{NA}, the default, includes if any aesthetics are mapped.
\code{FALSE} never includes, and \code{TRUE} always includes.
It can also be a named logical vector to finely select the aesthetics to
display.}

\item{inherit.aes}{If \code{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. \code{\link[=borders]{borders()}}.}

\item{geom, stat}{Override the default connection between \code{geom_bar()} and
\code{stat_count()}.}
}
\description{
There are two types of bar charts: \code{geom_bar()} and \code{geom_col()}.
\code{geom_bar()} makes the height of the bar proportional to the number of
cases in each group (or if the \code{weight} aesthetic is supplied, the sum
of the weights). If you want the heights of the bars to represent values
in the data, use \code{geom_col()} instead. \code{geom_bar()} uses \code{stat_count()} by
default: it counts the number of cases at each x position. \code{geom_col()}
uses \code{stat_identity()}: it leaves the data as is.
}
\details{
A bar chart uses height to represent a value, and so the base of the
bar must always be shown to produce a valid visual comparison.
Proceed with caution when using transformed scales with a bar chart.
It's important to always use a meaningful reference point for the base of the bar.
For example, for log transformations the reference point is 1. In fact, when
using a log scale, \code{geom_bar()} automatically places the base of the bar at 1.
Furthermore, never use stacked bars with a transformed scale, because scaling
happens before stacking. As a consequence, the height of bars will be wrong
when stacking occurs with a transformed scale.

By default, multiple bars occupying the same \code{x} position will be stacked
atop one another by \code{\link[=position_stack]{position_stack()}}. If you want them to be dodged
side-to-side, use \code{\link[=position_dodge]{position_dodge()}} or \code{\link[=position_dodge2]{position_dodge2()}}. Finally,
\code{\link[=position_fill]{position_fill()}} shows relative proportions at each \code{x} by stacking the
bars and then standardising each bar to have the same height.
}
\section{Orientation}{

This geom treats each axis differently and, thus, can thus have two orientations. Often the orientation is easy to deduce from a combination of the given mappings and the types of positional scales in use. Thus, ggplot2 will by default try to guess which orientation the layer should have. Under rare circumstances, the orientation is ambiguous and guessing may fail. In that case the orientation can be specified directly using the \code{orientation} parameter, which can be either \code{"x"} or \code{"y"}. The value gives the axis that the geom should run along, \code{"x"} being the default orientation you would expect for the geom.
}

\section{Aesthetics}{

\code{geom_bar()} understands the following aesthetics (required aesthetics are in bold):
\itemize{
\item \strong{\code{x}}
\item \strong{\code{y}}
\item \code{alpha}
\item \code{colour}
\item \code{fill}
\item \code{group}
\item \code{linetype}
\item \code{size}
}
Learn more about setting these aesthetics in \code{vignette("ggplot2-specs")}.


\code{geom_col()} understands the following aesthetics (required aesthetics are in bold):
\itemize{
\item \strong{\code{x}}
\item \strong{\code{y}}
\item \code{alpha}
\item \code{colour}
\item \code{fill}
\item \code{group}
\item \code{linetype}
\item \code{size}
}
Learn more about setting these aesthetics in \code{vignette("ggplot2-specs")}.


\code{stat_count()} understands the following aesthetics (required aesthetics are in bold):
\itemize{
\item \strong{\code{x} \emph{or} \code{y}}
\item \code{group}
\item \code{weight}
}
Learn more about setting these aesthetics in \code{vignette("ggplot2-specs")}.
}

\section{Computed variables}{

\describe{
\item{count}{number of points in bin}
\item{prop}{groupwise proportion}
}
}

\examples{
# geom_bar is designed to make it easy to create bar charts that show
# counts (or sums of weights)
g <- ggplot(mpg, aes(class))
# Number of cars in each class:
g + geom_bar()
# Total engine displacement of each class
g + geom_bar(aes(weight = displ))
# Map class to y instead to flip the orientation
ggplot(mpg) + geom_bar(aes(y = class))

# Bar charts are automatically stacked when multiple bars are placed
# at the same location. The order of the fill is designed to match
# the legend
g + geom_bar(aes(fill = drv))

# If you need to flip the order (because you've flipped the orientation)
# call position_stack() explicitly:
ggplot(mpg, aes(y = class)) +
 geom_bar(aes(fill = drv), position = position_stack(reverse = TRUE)) +
 theme(legend.position = "top")

# To show (e.g.) means, you need geom_col()
df <- data.frame(trt = c("a", "b", "c"), outcome = c(2.3, 1.9, 3.2))
ggplot(df, aes(trt, outcome)) +
  geom_col()
# But geom_point() displays exactly the same information and doesn't
# require the y-axis to touch zero.
ggplot(df, aes(trt, outcome)) +
  geom_point()

# You can also use geom_bar() with continuous data, in which case
# it will show counts at unique locations
df <- data.frame(x = rep(c(2.9, 3.1, 4.5), c(5, 10, 4)))
ggplot(df, aes(x)) + geom_bar()
# cf. a histogram of the same data
ggplot(df, aes(x)) + geom_histogram(binwidth = 0.5)
}
\seealso{
\code{\link[=geom_histogram]{geom_histogram()}} for continuous data,
\code{\link[=position_dodge]{position_dodge()}} and \code{\link[=position_dodge2]{position_dodge2()}} for creating side-by-side
bar charts.

\code{\link[=stat_bin]{stat_bin()}}, which bins data in ranges and counts the
cases in each range. It differs from \code{stat_count()}, which counts the
number of cases at each \code{x} position (without binning into ranges).
\code{\link[=stat_bin]{stat_bin()}} requires continuous \code{x} data, whereas
\code{stat_count()} can be used for both discrete and continuous \code{x} data.
}