Grouping Data
Grouping refers to the operation of putting data into groups so that the elements in each group share a common attribute.
The following illustration shows the results of grouping a sequence of characters. The key for each group is the character.
The standard query operator methods that group data elements are listed in the following section.
|
Method Name |
Description |
C# Query Expression Syntax |
Visual Basic Query Expression Syntax |
More Information |
|---|---|---|---|---|
|
GroupBy |
Groups elements that share a common attribute. Each group is represented by an IGrouping<TKey, TElement> object. |
group … by -or- group … by … into … |
Group … By … Into … |
|
|
ToLookup |
Inserts elements into a Lookup<TKey, TElement> (a one-to-many dictionary) based on a key selector function. |
Not applicable. |
Not applicable. |
The following code example uses the group by clause in C# or the Group By clause in Visual Basic to group integers in a list according to whether they are even or odd.
List<int> numbers = new List<int>() { 35, 44, 200, 84, 3987, 4, 199, 329, 446, 208 };
IEnumerable<IGrouping<int, int>> query = from number in numbers
group number by number % 2;
foreach (var group in query)
{
Console.WriteLine(group.Key == 0 ? "\nEven numbers:" : "\nOdd numbers:");
foreach (int i in group)
Console.WriteLine(i);
}
/* This code produces the following output:
Odd numbers:
35
3987
199
329
Even numbers:
44
200
84
4
446
208
*/
