How Can LINQ's GroupBy Operator Efficiently Aggregate Objects Based on Shared Property Values?

Efficient use of the Linq GroupBY operator to aggregate by the shared attribute value

In object -oriented programming, the situation of multiple objects sharing specific attributes is common. For example, the "PERSON" class contains "ID" and the car list. In order to clearly and efficiently aggregate a car associated with each unique ID, we can use Linq's "Groupby" operator.

linq groupby operating character

GroupBy operator divides the object sequence into a smaller group according to the value of the specified key. In our "Person" category, we can use the "Personid" property as a key to group objects. This will effectively create a structure similar to a dictionary, where the key is the only "Personid" value, and the value is a list of "car" values ​​associated with each "Personid".

code example

In order to group the "Person" object and retrieve the corresponding car list according to "Personid", we can use the following Linq query expression:

or, we can use non -query expressions to achieve the same results:

var results = from p in persons
              group p.car by p.PersonId into g
              select new { PersonId = g.Key, Cars = g.ToList() };

<<> Results

var results = persons.GroupBy(
    p => p.PersonId, 
    p => p.car,
    (key, g) => new { PersonId = key, Cars = g.ToList() });

"Results" variables will now contain a collection of an anonymous object, which has two attributes:

"Personid": The only ID of a person

"Cars": The list of all the car owned by the person

• By iteration of "Results" collection, we can get the required information of each unique "Personid".
• Other considerations

In order to be consistent with the naming agreement. It is recommended to use "Personid" instead of "Personid" when using the attribute name.

The comparison of the comparative

or, you can use the "Lookup" method instead of "Groupby" to achieve similar results. "LOOKUP" effectively creates a dictionary structure, where the key is the only "Personid" value, and the value is a collection of "car" values ​​associated with each "Personid". To use "LOOKUP" to retrieve the car's car, we can use the following syntax:

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