query LINQ per dividere un elenco ordinato in sottolisti di punti contigui secondo alcuni criteri

Question

Cercare aiuto durante la scrittura di una query LINQ su alcuni oggetti. Sento che se le mie capacità di LINQ fossero più ninja, potrei farlo con un po 'GroupBy/SelectMany (o qualcosa del genere ?!).

dichiarato genericamente, la domanda è: dato un elenco di oggetti in una sorta di ordine, dove ogni oggetto ha una bandiera, come faccio a dividere la lista in sotto-liste, dove ogni sottoelenco è tutti i punti contigui dove la bandiera è impostata?

Un modo imperativo di fare questo sarebbe come il seguente pseudocodice:

foreach object obj 
    if(obj.FlagSet) 
    add it to my currentsublist 
    else 
    skip to the next obj where FlagSet and start a new sublist 

Quindi, dato il seguente testo:

{1, Bandiera}, {2, Bandiera}, {3, noflag}, {4, Bandiera}, {5, noflag}, {6, Bandiera} ...

mi piacerebbe il seguente output:

Lista 1: {1, 2} Lista 2 : {4} List 3: {6}

E mi piacerebbe farlo funzionalmente tramite LINQ. Qualche idea?

(Ho guardato in giro prima, ma a tutte le domande che ho potuto vedere sembrava voler sia semplicemente un elenco di gruppo o di dividere in dimensioni uguali, che non è stato utile per me.)

Answer 1

Questo MSDN articolo fornisce il codice di gruppo da valori contigui:

http://msdn.microsoft.com/en-us/library/cc138361.aspx

ho riprodotto il codice dal link qui sopra in caso di link-rot:

public static class MyExtensions 
{ 
    public static IEnumerable<IGrouping<TKey, TSource>> ChunkBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector) 
    { 
     return source.ChunkBy(keySelector, EqualityComparer<TKey>.Default); 
    } 

    public static IEnumerable<IGrouping<TKey, TSource>> ChunkBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer) 
    { 
     // Flag to signal end of source sequence. 
     const bool noMoreSourceElements = true; 

     // Auto-generated iterator for the source array.  
     var enumerator = source.GetEnumerator(); 

     // Move to the first element in the source sequence. 
     if (!enumerator.MoveNext()) yield break; 

     // Iterate through source sequence and create a copy of each Chunk. 
     // On each pass, the iterator advances to the first element of the next "Chunk" 
     // in the source sequence. This loop corresponds to the outer foreach loop that 
     // executes the query. 
     Chunk<TKey, TSource> current = null; 
     while (true) 
     { 
      // Get the key for the current Chunk. The source iterator will churn through 
      // the source sequence until it finds an element with a key that doesn't match. 
      var key = keySelector(enumerator.Current); 

      // Make a new Chunk (group) object that initially has one GroupItem, which is a copy of the current source element. 
      current = new Chunk<TKey, TSource>(key, enumerator, value => comparer.Equals(key, keySelector(value))); 

      // Return the Chunk. A Chunk is an IGrouping<TKey,TSource>, which is the return value of the ChunkBy method. 
      // At this point the Chunk only has the first element in its source sequence. The remaining elements will be 
      // returned only when the client code foreach's over this chunk. See Chunk.GetEnumerator for more info. 
      yield return current; 

      // Check to see whether (a) the chunk has made a copy of all its source elements or 
      // (b) the iterator has reached the end of the source sequence. If the caller uses an inner 
      // foreach loop to iterate the chunk items, and that loop ran to completion, 
      // then the Chunk.GetEnumerator method will already have made 
      // copies of all chunk items before we get here. If the Chunk.GetEnumerator loop did not 
      // enumerate all elements in the chunk, we need to do it here to avoid corrupting the iterator 
      // for clients that may be calling us on a separate thread. 
      if (current.CopyAllChunkElements() == noMoreSourceElements) 
      { 
       yield break; 
      } 
     } 
    } 

    // A Chunk is a contiguous group of one or more source elements that have the same key. A Chunk 
    // has a key and a list of ChunkItem objects, which are copies of the elements in the source sequence. 
    class Chunk<TKey, TSource> : IGrouping<TKey, TSource> 
    { 
     // INVARIANT: DoneCopyingChunk == true || 
     // (predicate != null && predicate(enumerator.Current) && current.Value == enumerator.Current) 

     // A Chunk has a linked list of ChunkItems, which represent the elements in the current chunk. Each ChunkItem 
     // has a reference to the next ChunkItem in the list. 
     class ChunkItem 
     { 
      public ChunkItem(TSource value) 
      { 
       Value = value; 
      } 
      public readonly TSource Value; 
      public ChunkItem Next = null; 
     } 
     // The value that is used to determine matching elements 
     private readonly TKey key; 

     // Stores a reference to the enumerator for the source sequence 
     private IEnumerator<TSource> enumerator; 

     // A reference to the predicate that is used to compare keys. 
     private Func<TSource, bool> predicate; 

     // Stores the contents of the first source element that 
     // belongs with this chunk. 
     private readonly ChunkItem head; 

     // End of the list. It is repositioned each time a new 
     // ChunkItem is added. 
     private ChunkItem tail; 

     // Flag to indicate the source iterator has reached the end of the source sequence. 
     internal bool isLastSourceElement = false; 

     // Private object for thread syncronization 
     private object m_Lock; 

     // REQUIRES: enumerator != null && predicate != null 
     public Chunk(TKey key, IEnumerator<TSource> enumerator, Func<TSource, bool> predicate) 
     { 
      this.key = key; 
      this.enumerator = enumerator; 
      this.predicate = predicate; 

      // A Chunk always contains at least one element. 
      head = new ChunkItem(enumerator.Current); 

      // The end and beginning are the same until the list contains > 1 elements. 
      tail = head; 

      m_Lock = new object(); 
     } 

     // Indicates that all chunk elements have been copied to the list of ChunkItems, 
     // and the source enumerator is either at the end, or else on an element with a new key. 
     // the tail of the linked list is set to null in the CopyNextChunkElement method if the 
     // key of the next element does not match the current chunk's key, or there are no more elements in the source. 
     private bool DoneCopyingChunk { get { return tail == null; } } 

     // Adds one ChunkItem to the current group 
     // REQUIRES: !DoneCopyingChunk && lock(this) 
     private void CopyNextChunkElement() 
     { 
      // Try to advance the iterator on the source sequence. 
      // If MoveNext returns false we are at the end, and isLastSourceElement is set to true 
      isLastSourceElement = !enumerator.MoveNext(); 

      // If we are (a) at the end of the source, or (b) at the end of the current chunk 
      // then null out the enumerator and predicate for reuse with the next chunk. 
      if (isLastSourceElement || !predicate(enumerator.Current)) 
      { 
       enumerator = null; 
       predicate = null; 
      } 
      else 
      { 
       tail.Next = new ChunkItem(enumerator.Current); 
      } 

      // tail will be null if we are at the end of the chunk elements 
      // This check is made in DoneCopyingChunk. 
      tail = tail.Next; 
     } 

     // Called after the end of the last chunk was reached. It first checks whether 
     // there are more elements in the source sequence. If there are, it 
     // Returns true if enumerator for this chunk was exhausted. 
     internal bool CopyAllChunkElements() 
     { 
      while (true) 
      { 
       lock (m_Lock) 
       { 
        if (DoneCopyingChunk) 
        { 
         // If isLastSourceElement is false, 
         // it signals to the outer iterator 
         // to continue iterating. 
         return isLastSourceElement; 
        } 
        else 
        { 
         CopyNextChunkElement(); 
        } 
       } 
      } 
     } 

     public TKey Key { get { return key; } } 

     // Invoked by the inner foreach loop. This method stays just one step ahead 
     // of the client requests. It adds the next element of the chunk only after 
     // the clients requests the last element in the list so far. 
     public IEnumerator<TSource> GetEnumerator() 
     { 
      //Specify the initial element to enumerate. 
      ChunkItem current = head; 

      // There should always be at least one ChunkItem in a Chunk. 
      while (current != null) 
      { 
       // Yield the current item in the list. 
       yield return current.Value; 

       // Copy the next item from the source sequence, 
       // if we are at the end of our local list. 
       lock (m_Lock) 
       { 
        if (current == tail) 
        { 
         CopyNextChunkElement(); 
        } 
       } 

       // Move to the next ChunkItem in the list. 
       current = current.Next; 
      } 
     } 

     System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() 
     { 
      return GetEnumerator(); 
     } 
    } 
} 

Non è bello, ma funziona bene.

Nel tuo caso sarebbe qualcosa di simile:

myList.ChunkBy(o => o.FlagSet) 

Answer 2

Penso che il modo è di gestire lista di secondo e passato il resto basta aggiungere prima lista per lista finale e chiaro prima lista e aggiungere oggetto primo elenco quando il flag è impostato

Answer 3

Oltre a @spenders excellent link (+1!), mi piacerebbe aggiungere:

e 'abbastanza, e funziona bene:

• opera completamente in modo pigro
• è sicuro
• filo integra in LINQ di serie fornendo Chunk<> che implementa IGrouping<>
• ha alcuni problemi di stile (denominazione, la portata in eccesso, manca modificatore di sola lettura per m_lock; cose del genere)

L'unica vera lamentela che ho visto in questo momento è che non riesce a smaltire in modo proattivo gli enumeratori si ottiene dalla sorgente enumerabile.Qui è la mia correzione rilevante:

public static IEnumerable<IGrouping<TKey, TSource>> ChunkBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer) 
{ 
    // ... 
    using (var enumerator = source.GetEnumerator()) // <--- FIXED 
    { 

Aggiornamento

Qui è la mia fonte completamente modificata, fissa tutti i problemi sopra elencati. ** Questo rende anche Chunk<> usa e getta:

using System; 
using System.Collections.Generic; 
using System.Linq; 

namespace ChunkIt 
{ 
    public static class MyExtensions 
    { 
     public static IEnumerable<IGrouping<TKey, TSource>> ChunkBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector) 
     { 
      return source.ChunkBy(keySelector, EqualityComparer<TKey>.Default); 
     } 

     public static IEnumerable<IGrouping<TKey, TSource>> ChunkBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer) 
     { 
      const bool noMoreSourceElements = true; 

      using (var enumerator = source.GetEnumerator()) 
      { 
       if (!enumerator.MoveNext()) 
        yield break; 

       Chunk<TKey, TSource> current; 
       while (true) 
       { 
        var key = keySelector(enumerator.Current); 
        current = new Chunk<TKey, TSource>(key, enumerator, value => comparer.Equals(key, keySelector(value))); 

        yield return current; 

        if (current.CopyAllChunkElements() == noMoreSourceElements) 
         yield break; 
       } 
      } 
     } 

     class Chunk<TKey, TSource> : IGrouping<TKey, TSource>, IDisposable 
     { 
      class ChunkItem 
      { 
       public ChunkItem(TSource value) 
       { 
        Value = value; 
       } 
       public readonly TSource Value; 
       public ChunkItem Next; 
      } 

      private readonly TKey _key; 
      private IEnumerator<TSource> _enumerator; 
      private Func<TSource, bool> _predicate; 
      private readonly ChunkItem _head; 
      private ChunkItem _tail; 
      private bool _isLastSourceElement; 
      private readonly object _mLock; 

      public Chunk(TKey key, IEnumerator<TSource> enumerator, Func<TSource, bool> predicate) 
      { 
       _key = key; 
       _enumerator = enumerator; 
       _predicate = predicate; 

       _head = new ChunkItem(enumerator.Current); 

       _tail = _head; 

       _mLock = new object(); 
      } 

      private bool DoneCopyingChunk { get { return _tail == null; } } 

      private void CopyNextChunkElement() 
      { 
       _isLastSourceElement = !_enumerator.MoveNext(); 

       if (_isLastSourceElement || !_predicate(_enumerator.Current)) 
       { 
        _enumerator = null; 
        _predicate = null; 
       } 
       else 
       { 
        _tail.Next = new ChunkItem(_enumerator.Current); 
       } 

       _tail = _tail.Next; 
      } 

      internal bool CopyAllChunkElements() 
      { 
       while (true) 
        lock (_mLock) 
        { 
         if (DoneCopyingChunk) 
          return _isLastSourceElement; 

         CopyNextChunkElement(); 
        } 
      } 

      public TKey Key { get { return _key; } } 

      public IEnumerator<TSource> GetEnumerator() 
      { 
       ChunkItem current = _head; 

       while (current != null) 
       { 
        yield return current.Value; 

        lock (_mLock) 
         if (current == _tail) 
          CopyNextChunkElement(); 

        current = current.Next; 
       } 
      } 

      System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() 
      { 
       return GetEnumerator(); 
      } 

      #region Implementation of IDisposable 

      public void Dispose() 
      { 
       if (null!=_enumerator) 
        _enumerator.Dispose(); 

      } 

      #endregion 
     } 
    } 
} 

Answer 4

Con LINQ

var list = new[] 
{ 
    new KeyValuePair<string, string>("A", "We"), 
    new KeyValuePair<string, string>("A", "Think"), 
    new KeyValuePair<string, string>("A", "That"), 
    new KeyValuePair<string, string>("B", "Linq"), 
    new KeyValuePair<string, string>("C", "Is"), 
    new KeyValuePair<string, string>("A", "Really"), 
    new KeyValuePair<string, string>("B", "Cool"), 
    new KeyValuePair<string, string>("B", "!") 
}; 
var queryGroup = list.Select(data => data). 
    GroupBy(g => g.Key, //group key 
      i => i.Value //value 
    ); 
foreach (var group in queryGroup) 
{ 
    foreach (var data in group) 
    { 

    } 
} 
//even/odd grouping 
int groupCount = 2; 
var queryEvenOdd = list.Select((data, index) => new { data, index }). 
     GroupBy(
     g => g.index % groupCount,//group key 
     i => i.data //value 
     );