Getting your web application and R(Apache) to talk to each other

Here’s the situation. Web applications, built using a framework (e.g. Rails, Django) are great for fetching data from a database and rendering it. They’re not so great for crunching and charting the data. Conversely, R is great for crunching and charting, but doesn’t make for a great web application.

Index view for values

The idea then, is to let each do what it does best and enable the passing of data between them. There isn’t a whole lot of literature on this topic, but there are a couple of guides:

• In these seminar slides (PDF), Jeroen Ooms describes how data can be passed between a web browser and R. Briefly, he uses client-side javascript to format the data as a JSON string. Server-side R (RApache) then parses the POST variable using fromJSON() (in the rjson package), formats the results of an R function as JSON using toJSON() and sends them back to the browser.
• Slide 46 of this presentation by Mike Driscoll of Dataspora illustrates a different approach, where a Django-based web application sends data to RApache in CSV format.

As a first step in understanding all of this, we can build a small demo application using Rails (version 2.3.5), which serves both JSON and CSV. We’ll see if we can get that into R, then see if R can return results back to Rails, via RApache. Baby steps, so we’ll avoid the AJAX stuff for now and just use Rails rendering methods to serve JSON from a controller.