2-D Scatter Plot with Gradient Color Legend on Top

Question

I am trying to display a 2-D colored scatter plot -- i.e, Y as function of X with point colors driven by Z.

I would like the Z color-gradient legend to be on top, ideally below the main plot title.

I inspired myself from this SO with Z color-gradient on the right to derive the following function:

library(grDevices)
library(colorRamps)

# 2-dim scatter plot with color gradient legend on top.
scatterPlot2DWithColorLegend <- function(x, y, z, colorGradient, legendTitle=""
                                         , main="", xlab="", ylab="", pch=16, cex=1)
{
  parPrev <- par()
  nColorGradient <- length(colorGradient)
  labelRange <- zRange <- range(z)
  layout(matrix(1:2, nrow=2), widths = c(1), heights = c(1, 2), FALSE) # 2 plots, one above the other.
  # Plot legend first on top.
  plot(c(0, 1), c(0, 0.05), type = 'n', axes = F, xlab = '', ylab = '', main = legendTitle, cex.main=0.5)
  legend_image <- as.raster(matrix(colorGradient, nrow = 1))
  text(x = seq(0, 1, l = 5), y = 0.1 , labels = seq(labelRange[1], labelRange[2], l = 5), pos=1)
  rasterImage(legend_image, 0, 0, 1, 1)
  # Main plot second on bottom.
  if (1 < length(unique(zRange)))
    colVec = colorGradient[as.numeric(cut(z, nColorGradient))]
  else
    colVec = colorGradient[1]
  plot(x, y, col = colVec
       ,    main = main, xlab = xlab, ylab = ylab, pch = pch, cex = cex)
  par(parPrev)
}

This is a simple test code:

# Test data.
mdf <- data.frame(X=c(0:10))
mdf$Y <- mdf$X * 3
mdf$Z <- (mdf$X-5)^2

# Color gradient function.
colorGradient <- colorRampPalette(c("blue", "green", "yellow", "red"))(4)

# 2-D colored scatter plot.
scatterPlot2DWithColorLegend(mdf$X, mdf$Y, mdf$Z, colorGradient
                             , legendTitle="Z", main="Y vs. X with Z-Color", ylab="Y", xlab="X"
                             , pch=16, cex=0.7)

With my scatterPlot2DWithColorLegend function as above, I get:

enter image description here

I desire something like:

enter image description here

Can someone quickly offer an enhanced version of the scatterPlot2DWithColorLegend function or point me to an existing package/function that would get me what I want? Namely:

Main title above the color-gradient legend (Y vs. X with Z-Color).
Z-color gradient image smaller, height and width.
Z-color gradient Z-range on bottom (the Z-range does not currently show).
Z-color gradient legend to the left of Z-color gradient image as opposed to top (i.e., legendTitle="Z").
Significantly reduce spacing between main title, color-gradient legend, and the main scatter plot.

Obviously, I don't understand well R graphics. I am not familiar with the lattice, ggplot and the kinds either - the number of options appears overwhelming. I would like something simple that works I can reuse to get over this specific hump as this seems very basic.

Thanks in advance for any help.

You've got some good ggplot answers below, but this has also been similarly covered at this previous question. — thelatemail

Henrik Henrik · Accepted Answer · 2014-01-27T22:32:28

Here's a ggplot alternative:

ggplot(data = mdf, aes(x = X, y = Y, col = Z)) +
  geom_point() +
  scale_colour_gradientn(colours = colourGradient) +
  theme_bw() +
  theme(legend.position = "top") +
  ggtitle("Y vs. X with Z-Color")

enter image description here

2-D Scatter Plot with Gradient Color Legend on Top

1 Answers