Introduction for new R users"
In Ternary: Create Ternary and Holdridge Plots

Before you start, have you read the introduction to the Ternary package?

if (getRversion() < "3.6") {
  hcl.colors <- function(n, ...) {
    if (n == 4) {
      return(c("#A71B4B", "#F9C25C", "#81DEAD", "#584B9F"))
    } else {
      colorRampPalette(c("#4B0055", "#274983", "#008298", "#00B28A",
                         "#7ED357", "#FDE333"))(n)
    }
  }
}

This guide gives a brief example of using the "Ternary" package, using road casualty data from Great Britain.

First, we'll load and preview the data:

data("Seatbelts")

# View the first few entries:
head(Seatbelts)

For our example study, we'll explore the relative safety of car passengers through time by plotting the proportion of people killed or seriously injured in accidents who were drivers (column drivers), front-seat passengers (column front), or rear-seat passengers (column drivers).

Let's start by loading the "Ternary" package and plotting the data:

# Load the Ternary library
library("Ternary")

# Define our columns of interest:
seat <- c("drivers", "front", "rear")

# Extract and plot the data
TernaryPlot(alab = seat[1], blab = seat[2], clab = seat[3])
TernaryPoints(Seatbelts[, seat])

The law column takes the value 1 for months in which the wearing of a seatbelt was made compulsory in UK law. Let's explore the impact of this law by plotting data before and after the law with different symbols. R's plotting characters are numbered thus:

par(mar = c(0, 0, 0, 0))
plot(0:20, rep(2, 21), pch = 0:20,
     cex = 2, ylim = c(-1, 3), ann = FALSE)
text(0:20, rep(0, 21), 0:20)

Let's choose to plot a + (character 3) when seatbelts are legally required, and o (character 1) when they are not.

beltLawPch <- ifelse(Seatbelts[, "law"], 3, 1)

Let's also make the plot more readable by shrinking the margins:

# Shrink the margin so the plot's easier to read
par(mar = c(0, 0, 0, 0))

# Set up a blank plot
TernaryPlot(alab = seat[1], blab = seat[2], clab = seat[3])

# Add a legend
legend("topleft", c("Belt law", "No law"), pch = c(3, 1))

# Use our beltLawPch variable to style points
TernaryPoints(Seatbelts[, seat], pch = beltLawPch)

This seems to show a clear pattern: the seatbelt law led to a higher proportion of deaths and serious injuries occurring in the rear of cars.

Let's look for other trends through time by colouring each data point by when it was collected. Each row summarizes data for a consecutive month, so we can simply colour the points by row number.

Let's define a spectrum. The "viridis" colour scale is free from perceptual artefacts, is colour-blind friendly, and works when printed in greyscale.

nPoints <- nrow(Seatbelts)
rowCol <- hcl.colors(nPoints, palette = "viridis", alpha = 0.8)

Now we can plot our data:

par(mar = c(0, 0, 0, 0))

TernaryPlot(alab = seat[1], blab = seat[2], clab = seat[3])
legend("topleft", c("Belt law", "No law"), pch = c(3, 1))

# Add a legend for our colour scale
PlotTools::SpectrumLegend(palette = rowCol, legend = c("Dec 1984", "Jan 1969"))

# Use our rowCol variable to style points
TernaryPoints(Seatbelts[, seat], pch = beltLawPch,
              lwd = 2, # Use wider lines so points are clearer
              col = rowCol)

Our belt law appears to sit in the context of a longer term improvement in the relative safety of front-seat passengers. But how do we explain the scatter in the 'drivers' dimension? Let's try plotting seasonal variation:

# Define a suitable cyclical spectrum
fourSeasons <- hcl.colors(4, "Spectral")
monthCol <- colorRampPalette(fourSeasons[c(1:4, 1)])(13)[c(7:12, 1:6)]

par(mar = c(0, 0, 0, 0))

TernaryPlot(alab = seat[1], blab = seat[2], clab = seat[3])
legend("topleft", c("Belt law", "No law"), pch = c(3, 1))

legendMonths <- seq(1, 12, by = 2)
# Add a legend for our colour index
legend(
  "topright",
  bty = "n", # No frame
  pch = 15, # Filled square
  col = monthCol,
  legend = month.abb,
  title = "Month"
)

# Style points by law and month
TernaryPoints(Seatbelts[, seat], pch = beltLawPch,
              lwd = 2, # Use wider lines so points are clearer
              col = monthCol)

With or without seatbelts, drivers are in more relative danger in winter!

Now let's size each point by the number of casualties, scaled by distance driven. We'll need to zoom in closer to the plot to see this clearly.

par(mar = c(0, 0, 0, 0))

TernaryPlot(alab = seat[1], blab = seat[2], clab = seat[3],
            # Magnify the "action":
            xlim = c(0.055, 0.095), ylim = c(0.48, 0.52))

legend("topleft", c("No law", "Belt law"),
       col = 2:3, pch = 1, lwd = 2, lty = NA)
sizes <- c(3, 7, 12)
 scale <- 200
legend("topright", title = "Casualties / Mm", legend = sizes,
      pt.cex = sizes / 1000 * scale,
      pch = 1, lwd = 2, lty = NA)

# Style points according to casualties and the law
TernaryPoints(Seatbelts[, seat], pch = 1, lwd = 2,
              cex = Seatbelts[, "DriversKilled"] / Seatbelts[, "kms"] * scale,
              col = 2 + Seatbelts[, "law"])

The smaller size of points after mandatory seatbelt usage is evident.

Now let's plot the annual trend as a line, taking the values for each October as representative:

# Subset our data to extract only Octobers:
oct <- month.name == "October"
octBelts <- Seatbelts[oct, ]

par(mar = c(0, 0, 0, 0))
TernaryPlot(alab = seat[1], blab = seat[2], clab = seat[3],
            xlim = c(0.055, 0.095), ylim = c(0.48, 0.52),
            padding = 0.04)


TernarySegments(octBelts[-nrow(octBelts), seat], octBelts[-1, seat],
                col = rowCol, lwd = 2)

# Label each point by its year
TernaryText(octBelts[, seat], paste0("'", 69:84),
            font = 2, cex = 1.5,
            # Semi-transparent colours
            col = adjustcolor(rowCol[oct], alpha.f = 0.8))

# Provide a legend for our colour scheme
PlotTools::SpectrumLegend(
  "topright",
  bty = "n",
  palette = rowCol,
  legend = seq(1984, 1969, length.out = 4),
  title = "Year"
)