LINQ in c# : concise guide

LINQ (Language Integrated Query) is a uniform query syntax in C# to retrieve data from different sources and formats. LINQ generalizes the query interface by eliminating most of the hurdles to make raw data query/operation ready and as a result, LINQ returns an object for easy accessibility.

Required Namespace

using System;
using System.Linq;
using System.Collections.Generic;//for method LINQ

Three Parts of a Query Operation

At the time of actual query execution of dataQuery executes & creates IEnumerable<T> as result set which replaces dataQuery in foreach.

// 1. Obtain the data source
int[] dataList = new int[7] { 0, 1, 2, 3, 4, 5, 6 };
// 2. Query creation
var dataQuery = from num in dataList
                where (num % 2) == 0
                select num;
// 3. Query execution
foreach (int num in dataQuery)
{
    Console.Write("{0,1} ", num);
}

Two ways to write LINQ

List<string> cityList = new List<string>()
{“Mumbai”, “Pune”, “Chennai”, “Delhi”};
// way 1 - query syntax
var dataList1 = from city in cityList
                where city.Contains(“a”)
                select city;
foreach (var item in dataList1)
{
    Console.WriteLine(item);
}
// way 2 - method syntax (using extension method and lambda)
var dataList2 = cityList.Where(x => x.Contains(“a”)).Select(x => x);
foreach (var item in dataList2)
{
    Console.WriteLine(item);
}

Examples of LINQ

Where, OrderBy

var list1 = new List<string> { “Mike”, “John”, “Jane”, “Harvey”, “Rachel” };
//query syntax
var dataList1 = from x in list1
                where x.Contains("a")
                orderby x ascending
                select x;
//method syntax
var dataList2 = list1.Where(x => x.Contains("a"))
                .OrderBy(x => x)
                .Select(x => x);

Aggregate Function

int[] data = { 10, 20, 30, 40, 50 };
int result = data.Sum();//150
int result2 = data.Max();//50
int result3 = data.Min();//10
double result4 = data.Average();//30

Compare Multiple data lists

//compare two lists
var list1 = new List<int> { 5, 10, 15, 20, 25, 30, 35, 40 };
var list2 = new List<int> { 10, 20, 30, 40, 50 };
//query syntax
var dataList1 = from x in list1
                from y in list2
                where x < y
                select new { x, y };

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