Some sample mapper and reducer code. Feel free to fork and modify.
The mapper generates tuples of article:link, where article is the title of the article being looked at and link is every internal Wikipedia link that's referenced. The reducer takes sorted(!) tuples of article:link, article:link2 and makes them into lists article:link link2.
For example, say the article "Anarchy" links to two Wikipedia pages: Death and Destruction. The mapper would output: anarchy:death anarchy:destruction
The reducer outputs: anarchy death destruction
These scripts list the number of times that an article is cited in Wikipedia.
For example, the reducer outputs: 8813 anarchy