Flows between lodes or strata

geom_flow receives a dataset of the horizontal (x) and vertical (y, ymin, ymax) positions of the lodes of an alluvial diagram, the intersections of the alluvia with the strata. It reconfigures these into alluvial segments connecting pairs of corresponding lodes in adjacent strata and plots filled x-splines between each such pair, using a provided knot position parameter knot.pos, and filled rectangles at either end, using a provided width.

geom_flow(mapping = NULL, data = NULL, stat = "flow",
  position = "identity", width = 1/3, axis_width = NULL, knot.pos = 1/6,
  ribbon_bend = NULL, aes.flow = "forward", na.rm = FALSE,
  show.legend = NA, inherit.aes = TRUE, ...)

Arguments

mapping	Set of aesthetic mappings created by aes or 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.
stat	The statistical transformation to use on the data; override the default.
position	Position adjustment, either as a string, or the result of a call to a position adjustment function.
width	Numeric; the width of each stratum, as a proportion of the distance between axes. Defaults to 1/3.
axis_width	Deprecated; alias for width.
knot.pos	The horizontal distance between a stratum (width/2 from its axis) and the knot of the x-spline, as a proportion of the separation between strata. Defaults to 1/6.
ribbon_bend	Deprecated; alias for knot.pos.
aes.flow	Character; how inter-lode flows assume aesthetics from lodes. Options are "forward" and "backward".
na.rm	Logical: if FALSE, the default, NA lodes are not included; if TRUE, NA lodes constitute a separate category, plotted in grey (regardless of the color scheme).
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.
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. borders.
...	Additional arguments passed to layer.

Aesthetics

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

• x

• y

• ymin

• ymax

• alpha

• colour

• fill

• linetype

• size

• group

group is used internally; arguments are ignored.

See also

layer for additional arguments, and stat_stratum and geom_stratum for intra-axis boxes.

Examples

# use of strata and labels
ggplot(as.data.frame(Titanic),
       aes(weight = Freq,
           axis1 = Class, axis2 = Sex, axis3 = Age)) +
  geom_flow() +
  scale_x_continuous(breaks = 1:3, labels = c("Class", "Sex", "Age")) +
  geom_stratum() + geom_text(stat = "stratum", label.strata = TRUE) +
  ggtitle("Alluvial diagram of Titanic passenger demographic data")

# use of facets
ggplot(as.data.frame(Titanic),
       aes(weight = Freq,
           axis1 = Class, axis2 = Sex)) +
  geom_flow(aes(fill = Age)) +
  geom_stratum() + geom_text(stat = "stratum", label.strata = TRUE) +
  scale_x_continuous(breaks = 1:2, labels = c("Class", "Sex")) +
  facet_wrap(~ Survived, scales = "fixed")

# time series alluvia of WorldPhones data
wph <- as.data.frame(as.table(WorldPhones))
names(wph) <- c("Year", "Region", "Telephones")
ggplot(wph,
       aes(x = Year, alluvium = Region, weight = Telephones)) +
  geom_flow(aes(fill = Region, colour = Region), width = 0)

# rightward flow aesthetics for vaccine survey data
data(vaccinations)
levels(vaccinations$response) <- rev(levels(vaccinations$response))
ggplot(vaccinations,
       aes(x = survey, stratum = response, alluvium = subject,
           weight = freq, fill = response, label = round(a, 3))) +
  geom_lode() + geom_flow() +
  geom_stratum(alpha = 0) +
  geom_text(stat = "stratum")