David Esp Video Technical Blog

Slopegraph:

• Suppose you have a table of two columns) and that you want to show graphically how the (two) elements of each row correspond in terms of value. A Slopegraph is useful in this context.
• The originator, Edward Tufte (http://www.edwardtufte.com), says (http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0003nk&topic_id=1) “Slopegraphs compare changes over time for a list of nouns located on an ordinal or interval scale.”  Basically: Any time you’d use a line chart to show a progression of univariate data among multiple actors over time, you might have a good candidate for a slopegraph.  But some people have found it useful beyond this context.

Links:

•  First saw it here: http://alex4d.wordpress.com/2011/07/14/fpx-july-2011-price-changes/
  • This is a great example of its usefulness: price-spread variation (y-axis) over time (x-axis)
• Originator of this type of graph: http://charliepark.org/slopegraphs/
  • He has implemented it in various tools.
• An R-Function (sourcecode) to do it: https://github.com/bobthecat/codebox/blob/master/table.graph.r
  • I tried it and it works.
  • e.g. [   table.graph(data.frame(  Week1=0:9, Week2=c(1,3,5,7,11,13,17,19,23,29))  )   ]
    • http://msenux.redwoods.edu/math/R/dataframe.php explains how to create dataframes in R
• OT: No idea if it can be conveniently done in Apple Mac’s Grapher, but here’s a link about that app: http://guides.macrumors.com/Grapher