I am trying to group a sequence of Post
s by each distinct tag in the database.
public class Post
{
public string Title { get; set; }
public IEnumerable<string> Tags { get; set; }
public static IEnumerable<Post> SeedPosts()
{
yield return new Post { Title = "Foo", Tags = new[] { "Code" } };
yield return new Post { Title = "Foo1", Tags = new[] { "Code", "Productivity" } };
yield return new Post { Title = "Foo2", Tags = new[] { "Miscellaneous" } };
}
}
I want to take the result of SeedPosts
and produce the following output to a console application
Code
Foo
Foo1
Productivity
Foo1
Miscellaneous
Foo2
I am totally stumped but I will make an attempt to show you what I have tried so far.
I need the Key
to be of type string
but when I do this
posts.GroupBy(post => post.Tags);
the key is a of type IEnumerable<string>
. I understand that I am grouping by an IEnumerable<string>
, and so the key is an IEnuemrable<string>
, but I am generally stuck anyway.
Try this:
posts
.SelectMany(p => p.Tags.Select(t => new {Tag = t, Post = p}))
.GroupBy(_ => _.Tag)
.ToDictionary(_ => _.Key, _ => _.Select(p => p.Post.Title).ToArray());
Flatten the list either on a new list or the same one
var posts = new List<Post>();
posts.Add(new Post { Title = "Foo", Tags = new[] { "Code" } } );
posts.Add(new Post { Title = "Foo1", Tags = new[] { "Code", "Productivity" } });
posts.Add(new Post { Title = "Foo2", Tags = new[] { "Miscellaneous" } });
var flattendPosts = new List<Post>();
foreach (var post in posts)
{
var tags = post.Tags.Select(tag => tag);
for (int i = 0; i < tags.Count(); i++)
{
flattendPosts.Add(new Post { Title = post.Title, Tag = post.Tags[i] });
}
}
flattendPosts.GroupBy(post => post.Tags);
You don't really need a Dictionary
if all you want is outpuuting this to the console:
var posts = Post.SeedPosts();
var tagGroups = posts
.SelectMany(p => p.Tags, (post, tag) => new{Tag = tag, post.Title})
.GroupBy(pair => pair.Tag);
foreach (var tagGroup in tagGroups)
{
Console.WriteLine(tagGroup.Key);
foreach (var pair in tagGroup)
{
Console.WriteLine(" " + pair.Title);
}
}
Console.ReadKey();
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