Segments • ggdiagram

Setup

Packages

library(ggdiagram)
library(ggplot2)
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
library(ggtext)
library(ggarrow)
library(arrowheadr)

Base Plot

To avoid repetitive code, we make a base plot:


my_font <- "Roboto Condensed"
my_font_size <- 20
my_point_size <- 2
my_arrowhead <- arrowheadr::arrow_head_deltoid(2.1)

# my_colors <- viridis::viridis(2, begin = .25, end = .5)
my_colors <- c("#3B528B", "#21908C")

theme_set(
  theme_minimal(
    base_size = my_font_size,
    base_family = my_font) +
    theme(axis.title.y = element_text(angle = 0, vjust = 0.5)))

bp <- ggdiagram(
  font_family = my_font,
  font_size = my_font_size,
  point_size = my_point_size,
  linewidth = .5,
  theme_function = theme_minimal,
  axis.title.x =  element_text(face = "italic"),
  axis.title.y = element_text(
    face = "italic",
    angle = 0,
    hjust = .5,
    vjust = .5)) +
  scale_x_continuous(labels = WJSmisc::signs_centered,
                     limits = c(-4, 4)) +
  scale_y_continuous(labels = signs::signs,
                     limits = c(-4, 4))

Specifying a segment

A segment is a portion of a line between two points.

p1 <- ob_point(-3,-1)
p2 <- ob_point(3,3)
s1 <- ob_segment(p1, p2)

bp + s1 + p1 + p2

Figure 1: Plotting a segment and its endpoints

Styling a segment

The primary options for styling a segment are alpha, color, linetype, and linewidth. However, it can take any style from ggarrow::geom_arrow_segment

If you are not sure which properties can be set, you an see them in the @aesthetics@style slot.

s1@aesthetics@style
#>  [1] "alpha"            "arrow_head"       "arrow_fins"       "arrowhead_length"
#>  [5] "color"            "length_head"      "length_fins"      "lineend"         
#>  [9] "linejoin"         "linewidth"        "linewidth_fins"   "linewidth_head"  
#> [13] "linetype"         "resect"           "resect_fins"      "resect_head"     
#> [17] "stroke_color"     "stroke_width"

Styles can be specified when the segment is created.

s2 <- ob_segment(p1,p2, color = "green4")
bp + s2

Styles can be modified after the segment is created:

s2@linewidth <- 3
bp + s2

The as.geom function passes style arguments to the ggarrow::geom_arrow_segment function without modifying the segment’s style property:

bp +
  as.geom(s1, color = "red4")

Figure 2: Make s1 appear red temporarily using `as.geom` function

As an alternative, the geom property is a function that calls as.geom.

bp + s1@geom(color = "blue3")

Figure 3: Make s1 appear red temporarily via the `geom` property

To verify that s1 has not changed its color:

bp + s1

Figure 4: The `s1 object has not changed

A “pipe-friendly” way to modify any ggdiagram object is to use S7’s set_props function, which has been re-exported to ggdiagram for the sake of convenience. Like as.geom, this function does not modify s1, but unlike as.geom, set_props can be used to save a new object with the specified modifications by assigning it to a new variable. That is, as.geom creates a ggplot2 geom, whereas set_props will create a modified a ggdiagram object (or any other S7 class).

bp +
  s1 |>
    set_props(color = "red")

Features of a segment

Distance between points

s1@distance
#> [1] 7.211103

Alternately:

distance(s1)
#> [1] 7.211103

Line passing through the segment

The line that passes through the segment contains information about the segment, such as its slope, intercept, or angle.

To access the line that passes between both points:

s1@line
#> <ob_line>
#> @ slope     : num 0.667
#> @ intercept : num 1
#> @ xintercept: num -1.5
s1@line@slope
#> [1] 0.6666667
s1@line@intercept
#> [1] 1
s1@line@angle
#> 34°

Code

bp +
  s1@line |> set_props(color = "royalblue4") +
  s1@midpoint(position = c(0,1))@label(
    polar_just = ob_polar(s1@line@angle + degree(90), 1.5), 
    plot_point = TRUE) +
  ob_label(c(equation(s1@line), 
          paste0("Distance = ", round(s1@distance, 2))), 
        p = midpoint(s1), 
        vjust = c(-.2, 1.1), 
        angle = s1@line@angle)

Midpoints

By default, the midpoint function’s position argument is .5, which finds the point halfway between the point of a segment:

s1@midpoint()
#> <ob_point>
#> @ x: num 0
#> @ y: num 1
#> Other props: alpha, color, fill, shape, size, stroke, auto_label,
#>              bounding_box, length, r, theta, style, tibble, xy,
#>              geom, label, aesthetics

Code

bp +
  s1 +
  s1@midpoint()@label("Midpoint", hjust = 0, vjust = 1) +
  s1@midpoint(c(0, .5, 1))@label(plot_point = TRUE,
                             hjust = 1,
                             vjust = 0)

To find the midpoint 25% of the distance between the endpoints of segment:

s1@midpoint(position = .25)
#> <ob_point>
#> @ x: num -1.5
#> @ y: num 0
#> Other props: alpha, color, fill, shape, size, stroke, auto_label,
#>              bounding_box, length, r, theta, style, tibble, xy,
#>              geom, label, aesthetics

Code

bp +
  s1 +
  {p25 <- s1@midpoint(.25)} +
  p25@label(
    label = c(
      p25@auto_label,
      "Midpoint a quarter the<br>way between endpoints"
    ),
    vjust = c(0, 1),
    hjust = c(1, 0)
  ) +
  s1@midpoint(c(0, 1))@label(plot_point = TRUE,
                             hjust = 1,
                             vjust = 0)

Multiple midpoints can be specified:

bp + 
  s1 + 
    s1@midpoint(seq(0,1,.2))

A quick way to get the endpoints of a segment is to specify “midpoints” at positions 0 and 1:

bp + 
  s1 + 
  s1@midpoint(c(0,1))

Figure 9: Selecting a segment’s endpoints via the `midpoint` property.

Segment chains

If a point object with multiple points is placed in the p1 slot but the p2 slot is left empty, a series of segments chained together will be created.

bp + 
  ob_segment(ob_point(c(-4, -2, -1, 2,  4), 
                c(-2,  1, -2, 3, -3)))