Recursive Projection in Linq

gistfile1.cs

/// <summary>
/// Performs a projection on a heirachical sequence, without flattening
/// </summary>
/// <remarks>ie given an input type of X, each item of which has children which are also of type X,
/// execute a single selector across all X in the tree to retrieve a new target heirachy
/// </remarks>
public static IEnumerable<TOut> SelectRecurse<TIn,TOut>(IEnumerable<TIn> items, Func<TIn, IEnumerable<TIn>> childSelector, Func<TIn, IEnumerable<TOut>, TOut> selector){
	foreach(var item in items){
		
		var children = childSelector(item);
		var childrenMapped = SelectRecurse(children, childSelector, selector);
		
		var output = selector(item, childrenMapped);
		
		yield return output;
	}
}

Anytime I searched for 'recursive projection in Linq' I came across solutions that involved flattening, and (basically) projecting the flattened output. I needed to project but retain the hierarchy, ie project from one object graph to another, but do so as a simple lambda.