As a mathematical peasant who does modelling.<p># If you have a small data set - you set notation.<p># If you have 100s of larger data set - try to formulate your problem as a graph theory problem - Its easy to walk small graphs.<p># If you have 10,000 data points - start to think of your problem in terms of matrix.<p>I know there is going to strong disagreement about my rule of thumb but I found it useful for many problems.