(This article was first published on Revolutions, and kindly contributed to R-bloggers)
Foursquare, the mobile location-sharing app (of which I'm a big fan), has an excellent recommondation system. Based on your recent checkins, places your friends found popular, and even the time of day, Foursquare Explore will recommend a great place for a sushi lunch, or the best place to buy new shoes. This presentation from Foursquare engineer Ben Lee shows how R is part of the technology stack behind Explore (see slide 31). There are also several ggplot2 charts used to visualize Foursquare data, including this analysis of the rate of checkins to San Francisco's Tartine Bakery. (Yes, it's tough to get a table on the weekends!)
Foursquare Engineering: foursquare’s data and the Explore recommendation engine
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