How can I collapse a dataframe by some variables, taking mean across others
- by Alex Holcombe
I need to summarize a data frame by some variables, ignoring the others. This is sometimes referred to as collapsing. E.g. if I have a dataframe like this:
Widget Type Energy
egg 1 20
egg 2 30
jap 3 50
jap 1 60
Then collapsing by Widget, with Energy the dependent variable, Energy~Widget, would yield
Widget Energy
egg 25
jap 55
In Excel the closest functionality might be "Pivot tables" and I've worked out how to do it in python (http://alexholcombe.wordpress.com/2009/01/26/summarizing-data-by-combinations-of-variables-with-python/), and here's an example with R using doBy library to do something very related (http://www.mail-archive.com/[email protected]/msg02643.html), but is there an easy way to do the above? And even better is there anything built into the ggplot2 library to create plots that collapse across some variables?
