Alpha version of colorbar legend in ggplot2

The examples below show colorbar legends in ggplot2.

Please note that this is alpha version and it is not sure if this implementation appears in the future version of ggplot2.

I’m happy if you play with this function and report potential bugs and missing functions.

To test this, you need install Hadley’s scales package and my implementation based on Hadley’s ggplot2.

Here is a direct link to the tarball:

• scales: https://github.com/hadley/scales/tarball/master
• ggplot2 with colorbar: https://github.com/kohske/ggplot2/tarball/legend-colorbar

The colorbar is controlled by passing the legend_param argument to scale_{fill, colour}_XXX. XXX needs to be continuous family, e.g., discrete, etc.

The legend_param needs to be a list. Currently three elements is available.

1. colorbar (logical): draw colorbar if TRUE.
2. colorbar_nbin (integer): the number of division of colorbar, i.e., the resolution of the colorbar default: approx. 20).
3. colorbar_nbreaks (integer): the number of breaks of the colorbar (default: approx. 5).

The size of colorbar is controlled by theme – legend.key.size, legend.key.width, and legend.key.height.

The breaks and labels can be controlled via breaks and labels arguments in scale_*, this is same as normal legend.

Default legend

# default legend
p <- ggplot(melt(outer(1:4, 1:4)), aes(x=X1, y=X2)) + geom_tile(aes(fill=value))
p

Default colorbar legend

# colorbar legend (vertical)
p + scale_fill_continuous(legend_param=list(colorbar=T))

Default colorbar legend – horizontal

# colorbar legend (horizontal)
p + scale_fill_continuous(legend_param=list(colorbar=T)) + opts(legend.position="bottom", legend.direction="horizontal")

Specify the size of colorbar

# change the size of legend
p + scale_fill_continuous(legend_param=list(colorbar=T)) + opts(legend.key.width=unit(0.5, "line"), legend.key.height=unit(2, "line"))

Specify the number of breaks

# specify the number of breaks of legend
p + scale_fill_continuous(legend_param=list(colorbar=T, colorbar_nbreaks=10))

Manually specify the breaks

# manually specify the breaks
p + scale_fill_continuous(legend_param=list(colorbar=T), breaks=c(1,4,9,16))

Manually specify both breaks and labels

# manually specify the breaks and labels
p + scale_fill_continuous(legend_param=list(colorbar=T), breaks=c(1,4,9,16), labels=c("one^2", "two^2", "three^2", "four^2"))

Resolution of colorbar

# change the resolution of colorbar (default = 20)
p + scale_fill_continuous(legend_param=list(colorbar=T, colorbar_nbin=3))
p + scale_fill_continuous(legend_param=list(colorbar=T, colorbar_nbin=100))

Low resolution

High resolution

Combine with other legends

# combine with other scales with default scales
p + scale_fill_continuous(legend_param=list(colorbar=T)) + geom_point(aes(size=value))

Combine with colour and fill legends

# combine and merge colour and fill
p + geom_point(aes(y=X2+4, colour=value), size=10) + 
  scale_fill_continuous(legend_param=list(colorbar=T)) +
  scale_colour_continuous(legend_param=list(colorbar=T))

Seperately draw colour and fill colorbars

# combine but not merge colour and fill
ggplot(melt(outer(1:4, 1:4)), aes(x=X1, y=X2)) + geom_tile(aes(fill=value, colour=value), size=3) +
  scale_fill_continuous(name="fill", legend_param=list(colorbar=T)) +
  scale_colour_gradient(name="colour", low="pink", high="green", legend_param=list(colorbar=T))

Customize the color map

# use custom gradient (here jet colormap)
jet.colors <- colorRampPalette(c("#00007F", "blue", "#007FFF", "cyan", "#7FFF7F", "yellow", "#FF7F00", "red", "#7F0000"))
ggplot(melt(volcano), aes(x=X1, y=X2, fill=value)) + geom_tile() +
  scale_fill_gradientn(colours=jet.colors(7), legend_param=list(colorbar=T, colorbar_nbin=100))

Using plotmath expression for the legends

# plot math label by expression
p + scale_fill_continuous(
  expression(paste(alpha, beta, gamma)),
  legend_param=list(colorbar=T),
  breaks=c(1,16), labels=c(expression(1^2), expression(4^2)))

Specify the limits of the colorbar

# if the limits are pretty, then it looks like no expantion outside the limits
p + scale_fill_continuous(legend_param=list(colorbar=T, colorbar_nbin=100), limits=c(0,20))
# or set the breaks by using data range
p + scale_fill_continuous(legend_param=list(colorbar=T, colorbar_nbin=100),
  breaks=seq(range(p$data$value)[1], range(p$data$value)[2], length=5))