Sometimes you dont realy want to create ML algorithms from scratch. you just want to use them! unfortunantly not all of them are written for specific languages, for example, you can get an Information Gain / ID3 algorithm written in C#. However, you cant use it with numeric features in a multi-class problem. so the next best thing is to use weka’s IG which is written in Java (like all of weka), and if you dig enough on the weka wiki you will find that it is possible to use weka.jar from with in C#.
I have recently updated the wiki to reflect the proper workflow, and i managed to use a meta-classfier with SVM (SMO) using IG as the evaluator and Ranker as the search algorithm, in a 10 cross fold validation scenario.
details are here: http://weka.wikispaces.com/IKVM+with+Weka+tutorial