How to make a gradual color bar for representation of risk analysis results in R?

Question

I want to plot results of risk analysis that categorized by 4 levels (No risk, low, moderate and high risk) on gradual color bar (green-yellow-red). I thought about something like this (but I'm open for nicer suggestions.)

The input is something like this

results <- data.frame(matrix(nrow = 5,ncol = 0))
results$day <- c(1:5)
results$assessment <-c("Low","Moderate","High","Low","Moderate")

Answer 1

I will try to give a lot of detail with my answer.

I am assuming that you want just the colorbar and not the colorbar added to some other graph. That is what is created below.

0 Setup

library(fields)     ## for the colorbar function

## create the palette
myPalette = colorRampPalette(c("green", "yellow", "orange", "red"))

1 Create an empty plot.

plot(0:1, 0:1, type="n", bty="n", xaxs="i",
    xaxt="n", yaxt="n", xlab="", ylab="")   

When you run this, you should get an empty plot - no axes, nothing. Both x and y range from 0 to 1.

2 Create the color bar

colorbar.plot(0.5, 0.05, 1:100, col=myPalette(100),
    strip.width = 0.2, strip.length = 1.1)

3 Add the axis labels

axis(side=1, at=seq(0,1,1/3), tick=FALSE,
    labels=c("No Risk", "Low", "Moderate", "High Risk")) 

4 Add the arrow.

arrows(0.7, 0.18, 0.7, 0.1, length=0, lwd=8)
arrows(0.7, 0.18, 0.7, 0.09, length=0.1, lwd=3, angle=45)

This is a bit of a hack. If I made the lines in the arrow thick,
the arrowhead was rather blunt and ugly. So the first arrows statement makes a thick line with no arrowhead and the second one uses a thin line and adds a sharp arrowhead.

I have the arrow at 0.7. Adjust the x values to place it elsewhere.

Result