Essential Books

ToDictionary

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The ToDictionary() LINQ method can be used to generate a Dictionary<TKey, TElement> collection based on a given IEnumerable<T> source. 

IEnumerable<User> users = GetUsers();
Dictionary<int, User> usersById = users.ToDictionary(x => x.Id);

In this example, the single argument passed to ToDictionary is of type Func<TSource, TKey>, which returns the key for each element.

This is a concise way to perform the following operation: 

Dictionary<int, User> usersById = new Dictionary<int User>();
foreach (User u in users) 
{
  usersById.Add(u.Id, u);
}

You can also pass a second parameter to the ToDictionary method, which is of type Func<TSource, TElement> and returns the Value to be added for each entry. 

IEnumerable<User> users = GetUsers();
Dictionary<int, string> userNamesById = users.ToDictionary(x => x.Id, x => x.Name);

It is also possible to specify the IComparer that is used to compare key values. This can be useful when the key is a string and you want it to match case-insensitive. 

IEnumerable<User> users = GetUsers();
Dictionary<string, User> usersByCaseInsenstiveName = users.ToDictionary(x => x.Name, StringComparer.InvariantCultureIgnoreCase);

var user1 = usersByCaseInsenstiveName["john"];
var user2 = usersByCaseInsenstiveName["JOHN"];
user1 == user2; // Returns true

Note: the ToDictionary method requires all keys to be unique, there must be no duplicate keys. If there are, then an exception is thrown: ArgumentException: An item with the same key has already been added. If you have a scenario where you know that you will have multiple elements with the same key, then you are better off using ToLookup instead.

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LINQ Queries:
* LINQ Queries
* Chaining methods
* First FirstOrDefault Last LastOrDefault Single and SingleOrDefault
* Except
* SelectMany
* Any
* JOINS
* 0Skip and Take
* Zip
* 09Defining a variable inside a Linq query let keyword
* Range and Repeat
* All
* Basics
* Aggregate
* Distinct
* SelectMany Flattening a sequence of sequences
* Query collection by type cast elements to type
* GroupBy
* Enumerating the Enumerable
* Where
* Contains
* Using SelectMany instead of nested loops
* Using Range with various Linq methods
* Sum
* SkipWhile
* ToDictionary
* SequenceEqual
* Query Ordering - OrderBy ThenBy OrderByDescending ThenByDescending
* Any and FirstOrDefault - best practice
* GroupBy one or multiple fields
* OrderBy
* ElementAt and ElementAtOrDefault
* ToLookup
* Joining multiple sequences
* Joining on multiple keys
* DefaultIfEmpty
* GroupBy Sum and Count
* Count and LongCount
* Linq Quantifiers
* Build your own Linq operators for IEnumerableT
* GroupJoin with outer range variable
* Incrementally building a query
* Concat
* Reverse
* Union
* Select - Transforming elements
* OrderByDescending
* TakeWhile
* Select with FuncTSource int TResult selector - Use to get ranking of elements
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0 Getting Started With C#
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4 Equality Operator
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77 Read and Understand Stack trackes
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118 Task Parallel Library TPL Dataflow Constructs
119 Functional Programming
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121 Function with multiple return values
122 Binary Serialization
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124 IComparable
125 Accessing Databases
126 Using SQLite
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130 Structural Design Patterns
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132 Implementing Decorating Design Pattern
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137 Simulating C Unions with C# Structs
138 Reactive Extensions Rx
139 AsseblyInfo.cs examples
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144 Generating Random Numbers
145 Cryptography
146 Unsafe Code in .NET
147 C# Script
148 Runtime Compile
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150 .NET Compiler Platform Roslyn
151 Creating Own MessageBox in Windows Form Application
152 Including Font Resources
153 Garbage Collector
154 Windows Communication Foundation
155 Contributors