Slopegraphs

Compare values across two periods, with a line for each unit and a label at each end. Line crossings show changes in rank. Tufte's version prints the values directly, so the y axis is removed.

Usage

slopegraph(
  data,
  x,
  y,
  group,
  label_size = 2.8,
  line_colour = "grey45",
  linewidth = 0.35,
  point_size = 0,
  accuracy = 0.1,
  direction_colour = FALSE,
  min_gap = 0.03
)

Arguments

data

A data frame in long form: one row per unit per period.

x

Bare column name for the period. Coerced to a factor; its levels set the left-to-right order.

y

Bare column name for the value.

group

Bare column name identifying the unit.

label_size

Size of the printed labels. Defaults to 2.8.

line_colour

Colour of the connecting lines. Defaults to "grey45".

linewidth

Width of the connecting lines. Defaults to 0.35.

point_size

Size of the dots at each period. Set to 0 to omit them, as Tufte usually does.

accuracy

Rounding for the printed values, passed to label_number().

direction_colour

Logical. Colour lines by whether the unit rose or fell between the first and last period? Defaults to FALSE.

min_gap

Minimum vertical separation between labels, as a fraction of the y range. Labels closer than this are nudged apart. Set to 0 to disable. Adjust this for the font size and spacing in your figure.

Value

A ggplot object.

Details

The function accepts more than two periods, but labels only the first and last and warns about that limit.

Nearby labels are moved apart by default. If you have many similar values, you may still need a smaller label size or fewer units. Check the figure at its final size.

Examples

d <- data.frame(
  country = rep(c("Sweden", "Japan", "Chile", "Canada"), each = 2),
  year = rep(c("1970", "2020"), 4),
  value = c(30.1, 41.2, 20.7, 32.9, 22.5, 21.0, 31.0, 38.4)
)
slopegraph(d, year, value, country)