LINQ Tutorial
LINQ Useful Resources
Selected Reading
- LINQ - ASP.Net
- LINQ - Lambda Expressions
- LINQ - Entities
- LINQ - XML
- LINQ - Dataset
- LINQ - Objects
- LINQ - SQL
- LINQ - Query Operators
- LINQ - Environment Setup
- LINQ - Overview
- LINQ - Home
LINQ Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
LINQ - Query Operators
LINQ - Query Operators
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 capabipties pke filtering, sorting, projection, aggregation, etc.
LINQ standard query operators can be categorized into the following ones on the basis of their functionapty.
Filtering Operators
Join Operators
Projection Operations
Sorting Operators
Grouping Operators
Conversions
Concatenation
Aggregation
Quantifier Operations
Partition Operations
Generation Operations
Set Operations
Equapty
Element Operators
Filtering Operators
Filtering is an operation to restrict the result set such that it has only selected elements satisfying a particular condition.
| 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 abipty to be as a specified type | Not Apppcable | Not Apppcable |
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.
| 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.
| 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.
| 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 Apppcable | Not Apppcable |
Grouping Operators
The operators put data into some groups based on a common shared attribute.
| 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 Apppcable | Not Apppcable |
Conversions
The operators change the type of input objects and are used in a spanerse range of apppcations.
| Operator | Description | C# Query Expression Syntax | VB Query Expression Syntax |
|---|---|---|---|
| AsEnumerable | Returns the input typed as IEnumerable<T> | Not Apppcable | Not Apppcable |
| AsQueryable | A (generic) IEnumerable is converted to a (generic) IQueryable | Not Apppcable | Not Apppcable |
| Cast | Performs casting of elements of a collection to a specified type | Use an exppcitly typed range variable. Eg:from string str in words | From … As … |
| OfType | Filters values on basis of their , depending on their capabipty to be cast to a particular type | Not Apppcable | Not Apppcable |
| ToArray | Forces query execution and does conversion of a collection to an array | Not Apppcable | Not Apppcable |
| ToDictionary | On basis of a key selector function set elements into a Dictionary<TKey, TValue> and forces execution of a LINQ query | Not Apppcable | Not Apppcable |
| ToList | Forces execution of a query by converting a collection to a List<T> | Not Apppcable | Not Apppcable |
| ToLookup | Forces execution of a query and put elements into a Lookup<TKey, TElement> on basis of a key selector function | Not Apppcable | Not Apppcable |
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 duppcates.
| Operator | Description | C# Query Expression Syntax | VB Query Expression Syntax |
|---|---|---|---|
| Concat | Two sequences are concatenated for the formation of a single one sequence. | Not Apppcable | Not Apppcable |
Aggregation
Performs any type of desired aggregation and allows creating custom aggregations in LINQ.
| Operator | Description | C# Query Expression Syntax | VB Query Expression Syntax |
|---|---|---|---|
| Aggregate | Operates on the values of a collection to perform custom aggregation operation | Not Apppcable | Not Apppcable |
| Average | Average value of a collection of values is calculated | Not Apppcable | Aggregate … In … Into Average() |
| Count | Counts the elements satisfying a predicate function within collection | Not Apppcable | Aggregate … In … Into Count() |
| LonCount | Counts the elements satisfying a predicate function within a huge collection | Not Apppcable | Aggregate … In … Into LongCount() |
| Max | Find out the maximum value within a collection | Not Apppcable | Aggregate … In … Into Max() |
| Min | Find out the minimum value existing within a collection | Not Apppcable | Aggregate … In … Into Min() |
| Sum | Find out the sum of a values within a collection | Not Apppcable | 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.
| 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 Apppcable | Aggregate … In … Into All(…) |
| Any | Determines by searching a sequence that whether any element of the same satisfy a specified condition | Not Apppcable | 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 Apppcable | Not Apppcable |
Partition Operators
Divide an input sequence into two separate sections without rearranging the elements of the sequence and then returning one of them.
| 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 Apppcable | Skip |
| SkipWhile | Same as that of Skip with the only exception that number of elements to skip are specified by a Boolean condition | Not Apppcable | Skip While |
| Take | Take a specified number of elements from a sequence and skip the remaining ones | Not Apppcable | Take |
| TakeWhile | Same as that of Take except the fact that number of elements to take are specified by a Boolean condition | Not Apppcable | Take While |
Generation Operations
A new sequence of values is created by generational operators.
| Operator | Description | C# Query Expression Syntax | VB Query Expression Syntax |
|---|---|---|---|
| DefaultIfEmpty | When appped to an empty sequence, generate a default element within a sequence | Not Apppcable | Not Apppcable |
| Empty | Returns an empty sequence of values and is the most simplest generational operator | Not Apppcable | Not Apppcable |
| Range | Generates a collection having a sequence of integers or numbers | Not Apppcable | Not Apppcable |
| Repeat | Generates a sequence containing repeated values of a specific length | Not Apppcable | Not Apppcable |
Set Operations
There are four operators for the set operations, each yielding a result based on different criteria.
| Operator | Description | C# Query Expression Syntax | VB Query Expression Syntax |
|---|---|---|---|
| Distinct | Results a pst of unique values from a collection by filtering duppcate data if any | Not Apppcable | Distinct |
| Except | Compares the values of two collections and return the ones from one collection who are not in the other collection | Not Apppcable | Not Apppcable |
| Intersect | Returns the set of values found t be identical in two separate collections | Not Apppcable | Not Apppcable |
| Union | Combines content of two different collections into a single pst that too without any duppcate content | Not Apppcable | Not Apppcable |
Equapty
Compares two sentences (enumerable ) and determine are they an exact match or not.
| 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 Apppcable | Not Apppcable |
Element Operators
Except the DefaultIfEmpty, all the rest eight standard query element operators return a single element from a collection.
| Operator | Description | C# Query Expression Syntax | VB Query Expression Syntax |
|---|---|---|---|
| ElementAt | Returns an element present within a specific index in a collection | Not Apppcable | Not Apppcable |
| 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 Apppcable | Not Apppcable |
| First | Retrieves the first element within a collection or the first element satisfying a specific condition | Not Apppcable | Not Apppcable |
| FirstOrDefault | Same as First except the fact that it also returns a default value in case there is no existence of such elements | Not Apppcable | Not Apppcable |
| Last | Retrieves the last element present in a collection or the last element satisfying a specific condition | Not Apppcable | Not Apppcable |
| 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 Apppcable | Not Apppcable |
| Single | Returns the lone element of a collection or the lone element that satisfy a certain condition | Not Apppcable | Not Apppcable |
| SingleOrDefault | Same as Single except that it also returns a default value if there is no existence of any such lone element | Not Apppcable | Not Apppcable |
| DefaultIfEmpty | Returns a default value if the collection or pst is empty or null | Not Apppcable | Not Apppcable |