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 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.
| 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.
| 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 Applicable | Not Applicable |
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 Applicable | Not Applicable |
Conversions
The operators change the type of input objects and are used in a diverse range of applications.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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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