Use Linq to flatten a nested list instead of a foreach loop

Question

I have a recurring class - I've simplified it below.

public class SiloNode
{
    public string Key { get; private set; }
    public string Url { get; private set; }
    public List<SiloNode> Children { get; private set; }
}

Although, in theory, it could nest forever, the nodes will only ever go down two levels. So, a top-level node can have a child, but a child can't have a child.

I have a master list containing all of the top level nodes with their nested child nodes.

However, I need to get all nodes into a single flat list - node 1, followed by its children, followed by node 2 etc.

My knowledge in this area is limited, but I could do something like a foreach over the master list and create a new list, like this:

public IEnumerable<SiloNode> GetLinks(IEnumerable<SiloNode> masterList)
{
    var newList = new List<SiloNode>();

    foreach (var node in masterList)
    {
        newList.Add(node);
        newList.AddRange(node.Children);
    }

    return newList;
}

However, I know there's probably a much better way available but I just can't work out how to convert the foreach into a Linq statement that will do the same thing. In other words, select the parent and its children together.

Any help appreciated.

Answer 1

You can use SelectMany, just concat the single parent and it's children:

List<SiloNode> newList = masterList.SelectMany(n => new[]{ n }.Concat(n.Children)).ToList();