LINQ standard query operators implementation - a non-streaming

LINQ delay implementation are two, one is a stream, another non-streaming. Non-streaming operators must read all the data source, and in order to generate the result element.

Non-streaming operators include: GroupBy, OrderBy, OrderByDescending, Reverse, ThenBy, ThenByDescending

GroupBy

List<Pet> petsList =
    new List<Pet>{ new Pet { Name="Barley", Age=8.3 },
           new Pet { Name="Boots", Age=4.9 },
           new Pet { Name="Whiskers", Age=1.5 },
           new Pet { Name="Daisy", Age=4.3 } };

//public static IEnumerable<TResult> GroupBy<TSource, TKey, TElement, TResult>(this IEnumerable<TSource> source,
//Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, Func<TKey, IEnumerable<TElement>, TResult> resultSelector);
var query = petsList.GroupBy(pet => Math.Floor(pet.Age),pet=>pet.Age,(key,ages)=>new { 
    key,
    count=ages.Count(),
    min=ages.Min(),
    max=ages.Max()
});
         
foreach (var result in query)
{
    Console.WriteLine(result);               
}

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OrderBy, ascending

Pet[] pets = { new Pet { Name="Barley", Age=8 },
       new Pet { Name="Boots", Age=4 },
       new Pet { Name="Whiskers", Age=1 } };

//public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this IEnumerable<TSource> source,
//Func<TSource, TKey> keySelector);
IEnumerable<Pet> query = pets.OrderBy(pet => pet.Age);

foreach (Pet pet in query)
{
    Console.WriteLine("{0} - {1}", pet.Name, pet.Age);
}

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OrderByDescending, descending

List<decimal> decimals =
new List<decimal> { 6.2m, 8.3m, 0.5m, 1.3m, 6.3m, 9.7m };

IEnumerable<decimal> query =
    decimals.OrderByDescending(num=>num);

foreach (decimal num in query)
{
    Console.WriteLine(num);
}

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Reverse, reverse the order of elements in the sequence

char[] apple = { 'a', 'p', 'p', 'l', 'e' };

var reversed = apple.Reverse();

foreach (char chr in reversed)
{
    Console.Write(chr + " ");
}
Console.WriteLine();

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ThenBy perform subsequent sorting in ascending sequence of element

string[] fruits = { "grape", "passionfruit", "banana", "mango",
          "orange", "raspberry", "apple", "blueberry" };

//public static IOrderedEnumerable<TSource> ThenBy<TSource, TKey>(this IOrderedEnumerable<TSource> source, 
//    Func<TSource, TKey> keySelector);
IEnumerable<string> query =
    fruits.OrderBy(fruit => fruit.Length).ThenBy(fruit => fruit);

foreach (string fruit in query)
{
    Console.WriteLine(fruit);
}           

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ThenByDescending descending performed subsequent ordering of elements of a sequence

string[] fruits = { "apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE" };

//public static IOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this IOrderedEnumerable<TSource> source,
//Func<TSource, TKey> keySelector);
IEnumerable<string> query =
    fruits
    .OrderBy(fruit => fruit.Length)
    .ThenByDescending(fruit => fruit[0]);

foreach (string fruit in query)
{
    Console.WriteLine(fruit);
}

View Code