Jon Wood provides a very brief introduction to bag of words and how to produce them with ML.NET in this video.
Code – https://github.com/jwood803/MLNetExamples/blob/master/MLNetExamples/BagOfWords/Program.cs
Jon Wood shows us how to how to produce n-grams from text data in ML.NET.
Code – https://github.com/jwood803/MLNetExamples/blob/master/MLNetExamples/NGrams/Program.cs
N-Gram article – https://blog.xrds.acm.org/2017/10/introduction-n-grams-need/