Bars of a population pyramid

geom_pyramid() draws the bars of a population pyramid: one bar per age group on each side, extending away from a shared age axis. It counts rows, so it accepts individual records (aes(y = age, fill = sex)), and it sums a value when one is mapped, so it also accepts aggregated data (aes(x = n, y = age, fill = sex)). The bars are mirrored and stacked by position_pyramid(), and every other part of the plot (scales, facets, themes and further layers) comes from ggplot2 as usual.

Usage

geom_pyramid(
  mapping = NULL,
  data = NULL,
  stat = "pyramid",
  position = "pyramid",
  ...,
  denominator = NULL,
  just = 0.5,
  na.rm = FALSE,
  orientation = NA,
  show.legend = NA,
  inherit.aes = TRUE
)

stat_pyramid(
  mapping = NULL,
  data = NULL,
  geom = "bar",
  position = "pyramid",
  ...,
  denominator = NULL,
  na.rm = FALSE,
  orientation = NA,
  show.legend = NA,
  inherit.aes = TRUE
)

Arguments

mapping

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.

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A 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.

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

stat

The statistical transformation to use on the data for this layer. The default, "pyramid", is stat_pyramid().

position

A position adjustment. The default, "pyramid", is position_pyramid(); call it to set its arguments, for example position = position_pyramid(reverse = TRUE). To choose the side drawn on the left for every layer, use coord_pyramid(left = "Female").

...

Other arguments passed on to ggplot2::layer(), such as the bar width or fixed aesthetics like colour = "white".

denominator

NULL (the default) shows counts. "total" shows each bar as a proportion of all rows in the panel, and "side" as a proportion of the rows on its side.

just

Adjustment for column placement. Set to 0.5 by default, meaning that columns will be centered about axis breaks. Set to 0 or 1 to place columns to the left/right of axis breaks. Note that this argument may have unintended behaviour when used with alternative positions, e.g. position_dodge().

na.rm

If FALSE, the default, missing values are removed with a warning. If TRUE, missing values are silently removed.

orientation

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

show.legend

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. It can also be a named logical vector to finely select the aesthetics to display. To include legend keys for all levels, even when no data exists, use TRUE. If NA, all levels are shown in legend, but unobserved levels are omitted.

inherit.aes

If 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. annotation_borders().

geom

The geometric object used to display the data.

Value

A ggplot2 layer.

Aesthetics

Age goes on y, or on x for a vertical pyramid. The value axis is optional: when it is mapped, its values are summed within each age group, and when it is not, rows are counted. weight multiplies either. The side of each bar comes from side, or from fill when side is not mapped; see position_pyramid().

Computed variables

These can be used with ggplot2::after_stat():

• after_stat(count): the number of rows, or the sum of the value, in each age group. This is what the bars show by default.

• after_stat(prop): count as a proportion of all rows in the panel, or of the rows on the same side with denominator = "side". Each facet panel has its own denominator. The bars show prop whenever denominator is set.

See also

position_pyramid() to mirror other layers, and coord_pyramid() for the axes of a pyramid.

Examples

library(ggplot2)

pop <- data.frame(
  age = factor(rep(c("0-19", "20-39", "40-59", "60+"), 2)),
  sex = factor(rep(c("Male", "Female"), each = 4), c("Male", "Female")),
  n = c(220, 200, 160, 90, 210, 205, 170, 120)
)

# Aggregated data: the value is summed
ggplot(pop, aes(x = n, y = age, fill = sex)) +
  geom_pyramid() +
  coord_pyramid()


# Individual records: rows are counted
people <- pop[rep(seq_len(nrow(pop)), pop$n), c("age", "sex")]
ggplot(people, aes(y = age, fill = sex)) +
  geom_pyramid()


# Percentages of each side
ggplot(pop, aes(x = n, y = age, fill = sex)) +
  geom_pyramid(denominator = "side") +
  scale_x_continuous(labels = scales::label_percent()) +
  coord_pyramid() +
  labs(x = "Share of each sex")