Question

Is it possible to sum hierarchical data using .NET’s LINQ?

My data class looks like this:

class Node
{
    public decimal Amount;
    public IEnumerable<Node> Children { get; set; }
}

So I would have some data looks like this, but the tree could of course be arbitrarily deep.

var amounts = new Node
{
    Amount = 10;
    Children = new[]
    {
        new Node
        {
            Amount = 20
        },
        new Node
        {
            Amount = 30
        }
    }
};

It is possible sum all the amounts and get the result 60 with one simple LINQ query?

Answer 1

Technically you can write recursive lambda expressions, but you need to be insane or insanely bright to try (I haven’t figured out which). But you can cheat:

    Func<Node, decimal> nodeSum = null;
    nodeSum = node => {
        decimal result = node.Amount;
        if (node.Children != null) {
            result = result + node.Children.Sum(nodeSum);
        }
        return result;
    };
    var value = nodeSum(amounts);