How to implement decision tree with c# (visual studio 2008) - Help

Question

I have a decision tree that i need to turn to a code in C#

The simple way of doing it is using if-else statements but in this solution i will need to create 4-5 nested conditions.

I am looking for a better way to do it and so far i read a little bit about rule engines.

Do you have something else to suggest for an efficient way to develop decision tree with 4-5 nested conditions?

Answer 1

I implemented a simple decision tree as a sample in my book. The code is available online here, so perhaps you could use it as an inspiration. A decision is essentially represented as a class that has references to true branch and false branch and contains a function that does the test:

class DecisionQuery : Decision {
  public Decision Positive { get; set; }
  public Decision Negative { get; set; }
  // Primitive operation to be provided by the user
  public Func<Client, bool> Test { get; set; }

  public override bool Evaluate(Client client) {
    // Test a client using the primitive operation
    bool res = Test(client);
    // Select a branch to follow
    return res ? Positive.Evaluate(client) : Negative.Evaluate(client);
  }
}

Here, Decision is a base class that contains Evaluate method and the source contains one additional derived type that contains a final decision of the tree (yes/no). The type Client is a sample input data that you're analysing using the tree.

To create a decision tree, you can write something like:

var tree = new DecisionQuery {
    Test = (client) => client.Income > 40000,
    Positive = otherTree,
    Negative = someOtherTree
  };

If you just want to write five nested static if clauses then maybe just writing if is fine. The benefit of using a type like this one is that you can easily compose trees - e.g. reuse a part of a tree or modularize the construction.