How to use Linq to Group By individual items in a Collection?

I'm trying to find the most popular Tags that are used for a BlogPost.

eg.

public class BlogPost
{
    public int Id { get; set; }
    public IEnumerable<string> Tags { get; set; }
}

So I tried:

var tags = (from p in BlogPosts()
        group bp by bp.Tags into g
        select new {Tag = g.Key, Count = g.Count()})
    .OrderByDescending(o => o.Count)
    .Take(number);

but this doesn't compile. Error is: Cannot 开发者_运维问答implicitly convert type 'System.Linq.IQueryable<{Tag: System.IEnumerable<string>, Count: int}>' to 'System.Collections.Generic.Dictionary<string, int>'.

See how it's a list of strings? I was hoping to look through each tag in every blog post, and count the most popular ones.

I don't think you can group on a IEnumerable<string>, try this:

var tags = (from t in BlogPosts.SelectMany(p => p.Tags)
        group t by t into g
        select new {Tag = g.Key, Count = g.Count()})
    .OrderByDescending(o => o.Count)
    .Take(number);

SelectMany is the key here.

  var tags = posts
     .SelectMany (p => p.Tags)
     .GroupBy (t => t).Select(t => new {Tag = t.First (), Count=t.Count ()})
     .OrderBy(tc => tc.Count)
     .Select(tc => tc.Tag)
     .Take (15);

You want to group on singular tag names, not on whole lists of tags, which is what you are currently doing. Try this:

var tags =
    (from p in posts
    from tag in p.Tags
    group tag by tag into g
    select new {Tag = g.Key, Count = g.Count()})
.OrderByDescending(o => o.Count)
.Take(number);

Though this should do what you are asking for, it won't fix the compile error you're getting. That's somewhere else.