filter linq lookup based on values

Question

I would like to filter a linq Lookup based on its values:

the lookup:

ILookup<int, Article> lookup

here's what I've got so far which isn't working:

IList<int> cityIndexes = GetCityIndexesByNames(cities);    

lookup = lookup
                .Where(p => p.Any(x => cityIndexes.Contains((int)x.ArticleCity)))
                .SelectMany(l => l)
                .ToLookup(l => (int)l.ArticleParentIndex, l => l);

just to clarify: I want to get all the articles with a city index that is contained in the above city index list.

Answer 1

The problem with the code you posted, is that you're getting all the articles with the same ID as any article that has a matching city index. If you just unpack the groups first, there's no problem.

IList<int> cityIndexes = GetCityIndexesByNames(cities);

lookup = lookup
  .SelectMany(g => g)
  .Where(article => cityIndexes.Contains((int)article.ArticleCity)))
  .ToLookup(article => (int)article.ArticleParentIndex); 

Or

lookup =
(
  from g in lookup
  from article in g
  where cityIndexes.Contains((int)article.ArticleCity)))
  select article
).ToLookup(article => (int)article.ArticleParentIndex);