Linq To Objects Extension: Full Outer Join

I need a report which shows a comparison of the sales of each service with the previous year. Some services might be new and they don't appear in the previous year, others might be put off and so there are no sales for them in the current year. There can be services sold in both periods.

	public static IEnumerable<TResult> FullOuterJoin<TOuter, TInner, TKey, TResult>
	(this IEnumerable<TOuter> outer,
	IEnumerable<TInner> inner,
	Func<TOuter, TKey> outerKeySelector,
	Func<TInner, TKey> innerKeySelector,
	Func<TOuter, TInner, TResult> resultSelector)
	{
	// left side
	foreach (var current in outer)
	{
	if (!inner.Select(i => innerKeySelector(i)).Contains(outerKeySelector(current)))
	yield return resultSelector(current, default(TInner));
	}
	// middle side
	var innerJoin = outer.Join(inner, outerKeySelector, innerKeySelector, resultSelector);
	foreach (var current in innerJoin)
	yield return current;
	//right side
	foreach (var current in inner)
	{
	if (!outer.Select(i => outerKeySelector(i)).Contains(innerKeySelector(current)))
	yield return resultSelector(default(TOuter), current);
	}
	yield break;
	}
	public static IEnumerable<TResult> FullOuterJoin<TOuter, TInner, TKey, TResult>
	(this IEnumerable<TOuter> outer,
	IEnumerable<TInner> inner,
	Func<TOuter, TKey> outerKeySelector,
	Func<TInner, TKey> innerKeySelector,
	Func<TOuter, TInner, TResult> resultSelector,
	IEqualityComparer<TKey> comparer)
	{
	foreach (var current in outer)
	{
	if (!inner.Select(i => innerKeySelector(i)).Contains(outerKeySelector(current), comparer))
	yield return resultSelector(current, default(TInner));
	}
	var innerJoin = outer.Join(inner, outerKeySelector, innerKeySelector, resultSelector, comparer);
	foreach (var current in innerJoin)
	yield return current;
	foreach (var current in inner)
	{
	if (!outer.Select(i => outerKeySelector(i)).Contains(innerKeySelector(current), comparer))
	yield return resultSelector(default(TOuter), current);
	}
	yield break;
	}
	An a sample:
	var lastYearServices = new [] {
	new {
	Year = 2009,
	Services = new []{ new { Service = "A", Amount = 2009200m },
	new { Service = "B", Amount = 2009100m }}
	},
	new {
	Year = 2010,
	Services = new []{ new { Service = "X", Amount = 20102000m }}
	},
	new {
	Year = 2011,
	Services = new []{ new { Service = "AA", Amount = 2011200m }}
	}
	};
	var currentYearServices = new [] {
	new {
	Year = 2010,
	Services = new []{ new { Service = "B", Amount = 2010200m },
	new { Service = "C", Amount = 2010100m }}
	},
	new {
	Year = 2011,
	Services = new []{ new { Service = "X", Amount = 2011200m }}
	},
	new {
	Year = 2012,
	Services = new []{ new { Service = "AA", Amount = 2012200m },
	new { Service = "BB", Amount = 2012100m }}
	}
	};
	var query = from l in lastYearServices
	join c in currentYearServices on l.Year + 1 equals c.Year
	select new {
	Year = c.Year,
	Services = l.Services.FullOuterJoin(c.Services, ls => ls.Service, cs => cs.Service, (ls, cs) => new {
	LastYearAmount = ls != null ? ls.Amount : default(decimal?),
	CurrentYearAmount = cs != null ? cs.Amount : default(decimal?),
	Sevice = ls != null ? ls.Service : cs.Service
	})
	};
	query.Dump();

view raw FullOuterJoin.cs hosted with ❤ by GitHub