thomaskern / ggHorizon

cran package for creating horizon graphs with ggplot2

Horizon Graph

Prototype of a horizon graph implementation based on ggplot2.

The idea came up by Saito and Heer. See 2009's CHI paper Sizing the Horizon: The Effects of Chart Size and Layering on the Graphical Perception of Time Series Visualizations by Heer, Kong and Agrawala as well as 2005's Infovis paper Two-Tone Pseudo-Coloring: Compact Visualization for One-Dimensional Data. Proc. by Saito et al.

A smoothed horizon graph of the first 200 days of the EuStockMarkets dataset:

Usage

For the independent-geom-horizon.r file, use a data.frame of your liking and call plot_horizon. The parameters are as followed:

• data: only supports data.frame's. The order of the y-axis depends on the levels of the factor group. Required
• mapping: requires at least x,y and group. Required
• num.bands: number of bands
• smoothing: applies the smoothing function. Only valid values are loess and splines as characters
• band.colors: custom colours for the bands. Requires twice as many colours than num.bands. E.g. for num.bands=2 you would provide c(DarkNegative, BrightNegative, DarkPositive, BrightPositive)
• calculate.diff: uses the percental difference between x and x+1 for the y-axis
• loess.span: parameter span of loess(). Only applicable if loess is used for smoothing
• loess.interval: parameter interval of loess(). Only applicable if loess is used for smoothing
• spline.n: parameter n of spline(). Only applicable if spline is used for smoothing

plot_horizon returns a ggplot plot.

Examples

df = data.frame(group="A", x=0:9, y=c(0.2,0.8627684,0.92,-1,-0.8324571,-1.0061331,-0.5056517,0.1085939,0.6393061,-0.9098858))

plot_horizon(df,aes(x,y,group=group),2,smoothing="spline", spline.n=40)


df = data.frame(group=factor(rep(c("A","B"),each=10)), x=0:9, y=c(0.8, 0.4627684, 0.2072174, -1, -0.8324571, -1.0061331, -0.5056517, 0.3085939, 0.4383061, -0.9098858, 0.3, 0.1627684, 0.3072174, -0.3, -1.8324571, -1.0061331, -0.5056517, 0.1085939, 0.6393061, -0.9098858))

plot_horizon(df,aes(x,y,group=group),2, smoothing="spline", spline.n=40)

eu() is a function melting and adjusting the EuStockMarkets dataset to be used with ggplot2. Using it with plot_horizon:

plot_horizon(with(eu(),eu()[x <= 200,]), aes(x,y,group=group), num.steps=2, smoothing="loess", loess.span=0.2, loess.interval=0.1, calculate.diff=TRUE)

plot_horizon(with(eu(),eu()[x <= 200,]), aes(x,y,group=group), num.steps=2, smoothing="loess", loess.span=0.2, loess.interval=0.1)

To be done

Making a custom geom out of the standalone function proves difficult since changing the y-axis labels from within a geom is not allowed. Script geom-horizon.r provides the first draft of the custom geom.