I'm looking deeper into collaborative filtering. One really interesting paper is "A Comparative Study of Collaborative Filtering Algorithms" http://arxiv.org/pdf/1205.3193.pdf
In order to select which CF algorithm should be used the paper refers to the density of the dataset. What it doesn't do is explain how you actually calculate the density of your dataset.
So in the context of that above paper can anyone help explain to me how I would calculate the density of a dataset? The paper refers regularly density in the 1-5% range.