[GitHub] [arrow] Platob opened a new issue, #35243: [C#] Implement MapType

["Platob (via GitHub)" <gi...@apache.org>]

Platob opened a new issue, #35243:
URL: https://github.com/apache/arrow/issues/35243

   ### Describe the enhancement requested
   
   Hello,
   
   i started dev on new implementation of MapType, im wondering how it should be built ?
   
   I think is a list of Struct which are like `KeyValuePair` c# class
   
   ```csharp
   using System.Collections.Generic;
   
   namespace Apache.Arrow.Types
   {
       public class MapType : NestedType
       {
           public override ArrowTypeId TypeId => ArrowTypeId.Map;
           public override string Name => "map";
   
           public Field KeyField => Fields[0];
           public Field ValueField => Fields[0];
   
           public IArrowType ValueDataType => Fields[0].DataType;
   
           public MapType(IArrowType keyType, IArrowType valueType, bool nullable)
               : this(new Field("key", keyType, false), new Field("value", keyType, false), nullable)
           {
           }
   
           public MapType(Field keyField, Field valueField, bool nullable)
               : this(new StructType(new List<Field>() { keyField, valueField }), nullable)
           {
           }
   
           public MapType(StructType structType, bool nullable) : this(new ListType(new Field("key_value", structType, nullable)), nullable)
           {
           }
   
           public MapType(ListType listType, bool nullable) : this(new Field("key_values", listType, nullable))
           {
           }
   
           public MapType(Field keyValueField) : base(keyValueField)
           {
           }
   
           public override void Accept(IArrowTypeVisitor visitor) => Accept(this, visitor);
       }
   }
   ```
   
   ### Component(s)
   
   C#


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[GitHub] [arrow] westonpace commented on issue #35243: [C#] Implement MapType

["westonpace (via GitHub)" <gi...@apache.org>]

westonpace commented on issue #35243:
URL: https://github.com/apache/arrow/issues/35243#issuecomment-1516802780

   Yes, sounds like you have it correct.  Here is the comment from [schema.fbs](https://github.com/apache/arrow/blob/main/format/Schema.fbs#L104):
   
   > /// A Map is a logical nested type that is represented as
   ///
   /// List<entries: Struct<key: K, value: V>>
   ///
   /// In this layout, the keys and values are each respectively contiguous. We do
   /// not constrain the key and value types, so the application is responsible
   /// for ensuring that the keys are hashable and unique. Whether the keys are sorted
   /// may be set in the metadata for this field.
   ///
   /// In a field with Map type, the field has a child Struct field, which then
   /// has two children: key type and the second the value type. The names of the
   /// child fields may be respectively "entries", "key", and "value", but this is
   /// not enforced.
   ///
   /// Map
   /// 
   ///   - child[0] entries: Struct
   ///     -- child[0] key: K
   ///     -- child[1] value: V
   /// 
   /// Neither the "entries" field nor the "key" field may be nullable.
   ///
   /// The metadata is structured so that Arrow systems without special handling
   /// for Map can make Map an alias for List. The "layout" attribute for the Map
   /// field must have the same contents as a List.


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Re: [I] [C#] Implement MapType [arrow]

["lidavidm (via GitHub)" <gi...@apache.org>]

lidavidm closed issue #35243: [C#] Implement MapType
URL: https://github.com/apache/arrow/issues/35243


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