LINQ - Query Operators


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A set of extension methods forming a query pattern is known as LINQ Standard Query Operators. As building blocks of LINQ query expressions, these operators offer a range of query capabilities like filtering, sorting, projection, aggregation, etc.

LINQ standard query operators can be categorized into the following ones on the basis of their functionality.

  • Filtering Operators
  • Join Operators
  • Projection Operations
  • Sorting Operators
  • Grouping Operators
  • Conversions
  • Concatenation
  • Aggregation
  • Quantifier Operations
  • Partition Operations
  • Generation Operations
  • Set Operations
  • Equality
  • Element Operators

Filtering Operators

Filtering is an operation to restrict the result set such that it has only selected elements satisfying a particular condition.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
where Filter values based on a predicate function where Where
OfType Filter values based on their ability to be as a specified type Not Applicable Not Applicable

Join Operators

Joining refers to an operation in which data sources with difficult to follow relationships with each other in a direct way are targeted.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
Join The operator join two sequences on basis of matching keys join … in … on … equals … From x In …, y In … Where x.a = y.a
GroupJoin Join two sequences and group the matching elements join … in … on … equals … into … Group Join … In … On …

Projection Operations

Projection is an operation in which an object is transformed into an altogether new form with only specific properties.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
Select The operator projects values on basis of a transform function select Select
SelectMany The operator project the sequences of values which are based on a transform function as well as flattens them into a single sequence Use multiple from clauses Use multiple From clauses

Sorting Operators

A sorting operation allows ordering the elements of a sequence on basis of a single or more attributes.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
OrderBy The operator sort values in an ascending order orderby Order By
OrderByDescending The operator sort values in a descending order orderby ... descending Order By ... Descending
ThenBy Executes a secondary sorting in an ascending order orderby …, … Order By …, …
ThenByDescending Executes a secondary sorting in a descending order orderby …, … descending Order By …, … Descending
Reverse Performs a reversal of the order of the elements in a collection Not Applicable Not Applicable

Grouping Operators

The operators put data into some groups based on a common shared attribute.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
GroupBy Organize a sequence of items in groups and return them as an IEnumerable collection of type IGrouping<key, element> group … by -or- group … by … into … Group … By … Into …
ToLookup Execute a grouping operation in which a sequence of key pairs are returned Not Applicable Not Applicable

Conversions

The operators change the type of input objects and are used in a diverse range of applications.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
AsEnumerable Returns the input typed as IEnumerable<T> Not Applicable Not Applicable
AsQueryable A (generic) IEnumerable is converted to a (generic) IQueryable Not Applicable Not Applicable
Cast Performs casting of elements of a collection to a specified type Use an explicitly typed range variable. Eg:from string str in words From … As …
OfType Filters values on basis of their , depending on their capability to be cast to a particular type Not Applicable Not Applicable
ToArray Forces query execution and does conversion of a collection to an array Not Applicable Not Applicable
ToDictionary On basis of a key selector function set elements into a Dictionary<TKey, TValue> and forces execution of a LINQ query Not Applicable Not Applicable
ToList Forces execution of a query by converting a collection to a List<T> Not Applicable Not Applicable
ToLookup Forces execution of a query and put elements into a Lookup<TKey, TElement> on basis of a key selector function Not Applicable Not Applicable

Concatenation

Performs concatenation of two sequences and is quite similar to the Union operator in terms of its operation except of the fact that this does not remove duplicates.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
Concat Two sequences are concatenated for the formation of a single one sequence. Not Applicable Not Applicable

Aggregation

Performs any type of desired aggregation and allows creating custom aggregations in LINQ.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
Aggregate Operates on the values of a collection to perform custom aggregation operation Not Applicable Not Applicable
Average Average value of a collection of values is calculated Not Applicable Aggregate … In … Into Average()
Count Counts the elements satisfying a predicate function within collection Not Applicable Aggregate … In … Into Count()
LonCount Counts the elements satisfying a predicate function within a huge collection Not Applicable Aggregate … In … Into LongCount()
Max Find out the maximum value within a collection Not Applicable Aggregate … In … Into Max()
Min Find out the minimum value existing within a collection Not Applicable Aggregate … In … Into Min()
Sum Find out the sum of a values within a collection Not Applicable Aggregate … In … Into Sum()

Quantifier Operations

These operators return a Boolean value i.e. True or False when some or all elements within a sequence satisfy a specific condition.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
All Returns a value ‘True’ if all elements of a sequence satisfy a predicate condition Not Applicable Aggregate … In … Into All(…)
Any Determines by searching a sequence that whether any element of the same satisfy a specified condition Not Applicable Aggregate … In … Into Any()
Contains Returns a ‘True’ value if finds that a specific element is there in a sequence if the sequence doe not contains that specific element , ‘false’ value is returned Not Applicable Not Applicable

Partition Operators

Divide an input sequence into two separate sections without rearranging the elements of the sequence and then returning one of them.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
Skip Skips some specified number of elements within a sequence and returns the remaining ones Not Applicable Skip
SkipWhile Same as that of Skip with the only exception that number of elements to skip are specified by a Boolean condition Not Applicable Skip While
Take Take a specified number of elements from a sequence and skip the remaining ones Not Applicable Take
TakeWhile Same as that of Take except the fact that number of elements to take are specified by a Boolean condition Not Applicable Take While

Generation Operations

A new sequence of values is created by generational operators.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
DefaultIfEmpty When applied to an empty sequence, generate a default element within a sequence Not Applicable Not Applicable
Empty Returns an empty sequence of values and is the most simplest generational operator Not Applicable Not Applicable
Range Generates a collection having a sequence of integers or numbers Not Applicable Not Applicable
Repeat Generates a sequence containing repeated values of a specific length Not Applicable Not Applicable

Set Operations

There are four operators for the set operations, each yielding a result based on different criteria.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
Distinct Results a list of unique values from a collection by filtering duplicate data if any Not Applicable Distinct
Except Compares the values of two collections and return the ones from one collection who are not in the other collection Not Applicable Not Applicable
Intersect Returns the set of values found t be identical in two separate collections Not Applicable Not Applicable
Union Combines content of two different collections into a single list that too without any duplicate content Not Applicable Not Applicable

Equality

Compares two sentences (enumerable ) and determine are they an exact match or not.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
SequenceEqual Results a Boolean value if two sequences are found to be identical to each other Not Applicable Not Applicable

Element Operators

Except the DefaultIfEmpty, all the rest eight standard query element operators return a single element from a collection.

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Operator Description C# Query Expression Syntax VB Query Expression Syntax
ElementAt Returns an element present within a specific index in a collection Not Applicable Not Applicable
ElementAtOrDefault Same as ElementAt except of the fact that it also returns a default value in case the specific index is out of range Not Applicable Not Applicable
First Retrieves the first element within a collection or the first element satisfying a specific condition Not Applicable Not Applicable
FirstOrDefault Same as First except the fact that it also returns a default value in case there is no existence of such elements Not Applicable Not Applicable
Last Retrieves the last element present in a collection or the last element satisfying a specific condition Not Applicable Not Applicable
LastOrDefault Same as Last except the fact that it also returns a default value in case there is no existence of any such element Not Applicable Not Applicable
Single Returns the lone element of a collection or the lone element that satisfy a certain condition Not Applicable Not Applicable
SingleOrDefault Same as Single except that it also returns a default value if there is no existence of any such lone element Not Applicable Not Applicable
DefaultIfEmpty Returns a default value if the collection or list is empty or null Not Applicable Not Applicable


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