Linq-query-operators
提供：Dev Guides
LINQ-クエリ演算子
クエリパターンを形成する一連の拡張メソッドは、LINQ Standard Query Operatorsと呼ばれます。 LINQクエリ式の構成要素として、これらの演算子はフィルタリング、並べ替え、投影、集計などのさまざまなクエリ機能を提供します。
LINQ標準クエリ演算子は、機能に基づいて次のカテゴリに分類できます。
- フィルタリング演算子
- 結合演算子
- 投影操作
- ソート演算子
- グループ化演算子
- コンバージョン数
- 連結
- 集約
- 量指定子の操作
- パーティション操作
- 発電事業
- セット操作
- 平等
- 要素演算子
フィルタリング演算子
フィルタリングは、特定の条件を満たす選択された要素のみを持つように結果セットを制限する操作です。
link：/linq/linq_filtering_operators [例を表示]
| 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 |
結合演算子
結合とは、相互の関係を直接的な方法で追跡することが困難なデータソースを対象とする操作を指します。
link：/linq/linq_join_operators [例を表示]
| 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 … |
投影操作
投影とは、オブジェクトを特定のプロパティのみを持つまったく新しいフォームに変換する操作です。
リンク：/linq/linq_projection_operations [例を表示]
| 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 |
ソート演算子
ソート操作を使用すると、単一または複数の属性に基づいてシーケンスの要素を並べることができます。
link：/linq/linq_sorting_operators [例を表示]
| 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 |
グループ化演算子
オペレーターは、共通の共有属性に基づいていくつかのグループにデータを入れます。
link：/linq/linq_grouping_operators [例を表示]
| 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 |
コンバージョン数
演算子は入力オブジェクトのタイプを変更し、さまざまなアプリケーションで使用されます。
link：/linq/linq_conversions [例を表示]
| 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 |
連結
2つのシーケンスの連結を実行します。これは、重複を削除しないという事実を除いて、操作に関してはUnion演算子に非常に似ています。
link：/linq/linq_concatenation [例を表示]
| 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 |
集約
任意のタイプの必要な集計を実行し、LINQでカスタム集計を作成できます。
link：/linq/linq_aggregation [例を表示]
| 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() |
量指定子の操作
これらの演算子はブール値、つまり シーケンス内の一部またはすべての要素が特定の条件を満たす場合に真または偽。
link：/linq/linq_quantifier_operations [例を表示]
| 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 |
パーティション演算子
入力シーケンスを2つのセクションに分割します。シーケンスの要素を並べ替えてから1つを返すことはありません。
link：/linq/linq_partition_operators [例を表示]
| 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 |
発電事業
世代演算子によって新しい値のシーケンスが作成されます。
リンク：/linq/linq_generation_operations [例を表示]
| 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 |
セット操作
集合演算には4つの演算子があり、それぞれ異なる基準に基づいて結果を生成します。
link：/linq/linq_set_operations [例を表示]
| 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 |
平等
2つの文（列挙可能）を比較し、それらが完全に一致するかどうかを判断します。
link：/linq/linq_equality [例を表示]
| 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 |
要素演算子
DefaultIfEmptyを除き、残りの8つの標準クエリ要素演算子はすべて、コレクションから単一の要素を返します。
link：/linq/linq_element_operators [例を表示]
| 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 |
