position_attractsegment {ggarchery}

Nudge points towards each other along a line

Description

This position function is primarily intended for use with ggplot2::geom_segment() or geom_arrowsegment(), and solves the problem that the user may, for reasons of clarity or aesthetics, not want their arrows to actually start or end at the position that they are "pointing from" or "pointing to". It works by shifting the points towards each other along the line joining them, by either a proportional amount or a fixed distance.

Usage

position_attractsegment(
  start_shave = 0,
  end_shave = 0,
  type_shave = c("proportion", "distance")
)

Arguments

start_shave, end_shave

The amount of distance to "shave" off the line between (x, y) and (xend, yend), at, respectively, the start and the end. Can be zero; cannot be negative. Units are determined by type_shave.

type_shave

If "proportion" (the default) then this is a proportion of the total line length. If "distance" then it is instead the raw distance along the line. The is only really recommended in combination with ggplot2::coord_fixed(); results can be quite odd otherwise.

Value

A ggproto object

Examples

 library(ggplot2)
 library(magrittr)
 library(tidyr)

 # Generate some dummy data

 ten.points <- data.frame(line.no = rep(1:5, each = 2), x = runif(10), y = runif(10),
                          position = rep(c("start", "end"), 5))
 five.segments <- ten.points %>% pivot_wider(names_from = position, values_from = c(x,y))

 # Ten percent off the start and end

 ggplot(five.segments) +
   geom_point(data = ten.points, aes(x = x, y = y)) +
   geom_arrowsegment(aes(x = x_start, xend = x_end, y = y_start, yend = y_end),
                     position = position_attractsegment(start_shave = 0.1, end_shave = 0.1))

 # Absolute distance of 0.02 at the end only

 ggplot(five.segments) +
   geom_point(data = ten.points, aes(x = x, y = y)) +
   geom_arrowsegment(aes(x = x_start, xend = x_end, y = y_start, yend = y_end),
                     position = position_attractsegment(end_shave = 0.02,
                                                        type_shave = "distance")) +
   coord_fixed()