How Can LINQ Group Objects into a Hierarchical List Structure?

Group objects into hierarchical list structures using LINQ

Suppose you have a set of objects that have properties that classify them. For example, imagine that you have a set of users that belong to different groups. To organize and analyze data efficiently, you may want to group users based on their group associations.

In this example, we have a class called User with attributes including UserID, UserName, and GroupID. Let's say we have a list of users that looks like this:

<code class="language-csharp">List<User> userList = new List<User>();
userList.Add(new User { UserID = 1, UserName = "UserOne", GroupID = 1 });
userList.Add(new User { UserID = 2, UserName = "UserTwo", GroupID = 1 });
userList.Add(new User { UserID = 3, UserName = "UserThree", GroupID = 2 });
userList.Add(new User { UserID = 4, UserName = "UserFour", GroupID = 1 });
userList.Add(new User { UserID = 5, UserName = "UserFive", GroupID = 3 });
userList.Add(new User { UserID = 6, UserName = "UserSix", GroupID = 3 });</code>

Our goal is to convert this list into a hierarchical structure that groups together users who belong to the same group. The desired output looks like:

<code>GroupedUserList
    UserList
        UserID = 1, UserName = "UserOne", GroupID = 1
        UserID = 2, UserName = "UserTwo", GroupID = 1
        UserID = 4, UserName = "UserFour", GroupID = 1
    UserList
        UserID = 3, UserName = "UserThree", GroupID = 2
    UserList
        UserID = 5, UserName = "UserFive", GroupID = 3
        UserID = 6, UserName = "UserSix", GroupID = 3</code>

Using LINQ’s powerful aggregation capabilities, we can achieve this grouping using the following code:

<code class="language-csharp">var groupedCustomerList = userList
    .GroupBy(u => u.GroupID)
    .Select(grp => grp.ToList())
    .ToList();</code>

The

GroupBy method classifies users based on their GroupID attributes. It generates a collection of groups, where each group represents a unique GroupID. The Select method further converts these groups into lists of users, giving us a hierarchical structure that nests lists of users within each group.

By using this LINQ query, you can effectively organize data into meaningful groups, thereby enhancing your data analysis and manipulation capabilities.

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