Question

我有一个元素数组，其中元素具有Flagged布尔值。

1 flagged
2 not flagged
3 not flagged
4 flagged
5 not flagged
6 not flagged
7 not flagged
8 flagged
9 not flagged

我想根据标记的指标将其分解为数组

输出＆gt;

array 1 {1,2,3}
array 2 {4,5,6,7}
array 3 {8,9}

Answer 1

Linq没有这方面的操作符，但是我编写了一个你可以使用的扩展方法（在提交到MoreLinq的过程中，你也应该检查）：

使用下面的操作符，您可以写：

var result = 
   items.Segment( (item,prevItem,idx) => item.Flagged )
        .Select( seq => seq.ToArray() )  // converts each sequence to an array
        .ToList();

这是扩展方法的代码：

public static IEnumerable<IEnumerable<T>> Segment<T>(IEnumerable<T> sequence, Func<T, T, int, bool> newSegmentIdentifier) 
     { 
         var index = -1; 
         using (var iter = sequence.GetEnumerator()) 
         { 
             var segment = new List<T>(); 
             var prevItem = default(T); 

             // ensure that the first item is always part 
             // of the first segment. This is an intentional 
             // behavior. Segmentation always begins with 
             // the second element in the sequence. 
             if (iter.MoveNext()) 
             { 
                 ++index; 
                 segment.Add(iter.Current); 
                 prevItem = iter.Current; 
             } 

             while (iter.MoveNext()) 
             { 
                 ++index; 
                 // check if the item represents the start of a new segment 
                 var isNewSegment = newSegmentIdentifier(iter.Current, prevItem, index); 
                 prevItem = iter.Current; 

                 if (!isNewSegment) 
                 { 
                     // if not a new segment, append and continue 
                     segment.Add(iter.Current); 
                     continue; 
                 } 
                 yield return segment; // yield the completed segment 

                 // start a new segment... 
                 segment = new List<T> { iter.Current }; 
             } 
             // handle the case of the sequence ending before new segment is detected 
             if (segment.Count > 0) 
                 yield return segment; 
         } 
     }

Answer 2

我遇到了类似的问题，并使用GroupBy和闭包来解决它。

//sample data
var arrayOfElements = new[] {
    new { Id = 1, Flagged = true },
    new { Id = 2, Flagged = false },
    new { Id = 3, Flagged = false },
    new { Id = 4, Flagged = true },
    new { Id = 5, Flagged = false },
    new { Id = 6, Flagged = false },
    new { Id = 7, Flagged = false },
    new { Id = 8, Flagged = true },
    new { Id = 9, Flagged = false }
};

//this is the closure which will increase each time I see a flagged
int flagCounter = 0;

var query = 
    arrayOfElements.GroupBy(e => 
        {
            if (e.Flagged)
                flagCounter++;
            return flagCounter;
        });

它的作用是对int（flagCounter）进行分组，每次找到Flagged元素时都会增加。
请注意，这不适用于AsParallel()。

测试结果：

foreach(var group in query)
{
    Console.Write("\r\nGroup: ");
    foreach (var element in group)
        Console.Write(element.Id);
}

输出：

组：123
  组：4567
  组：89

Answer 3

考虑到：

var arrayOfElements = new[] {
    new { Id = 1, Flagged = true },
    new { Id = 2, Flagged = false },
    new { Id = 3, Flagged = false },
    new { Id = 4, Flagged = true },
    new { Id = 5, Flagged = false },
    new { Id = 6, Flagged = false },
    new { Id = 7, Flagged = false },
    new { Id = 8, Flagged = true },
    new { Id = 9, Flagged = false }
};

你可以写：

var grouped = 
    from i in arrayOfElements
    where i.Flagged
    select 
        (new[] { i.Id })
        .Union(arrayOfElements.Where(i2 => i2.Id > i.Id).TakeWhile(i2 => !i2.Flagged).Select(i2 => i2.Id))
        .ToArray();

如果您的元素按Id属性排序，则此方法有效。如果他们不这样做，你将不得不在原始阵列上注入一个序列，这也很容易用linq做，所以你会得到一个序列。

此外，更好的选择应该是：

// for each flagged element, slice the array,
// starting on the flagged element until the next flagged element
var grouped = 
    from i in arrayOfElements
    where i.Flagged
    select 
        arrayOfElements
            .SkipWhile(i2 => i2 != i)
            .TakeWhile(i2 => i2 == i || !i2.Flagged)
            .Select(i2 => i2.Id)
            .ToArray();

请注意，这些答案都是使用纯粹的linq。

Answer 4

我不认为LINQ是完成此任务的正确工具。那怎么样：

public static List<List<T>> PartitionData<T>(T[] arr, Func<T, bool> flagSelector){
    List<List<T>> output = new List<List<T>>();
    List<T> partition = null;
    bool first = true;

    foreach(T obj in arr){
        if(flagSelector(obj) || first){
            partition = new List<T>();
            output.Add(partition);
            first = false;
        }
        partition.Add(obj);
    }

    return output;
}

一个小例子，来自FábioBatistas的数据发布：

var arrayOfElements = new[] {
    new { Id = 1, Flagged = true },
    new { Id = 2, Flagged = false },
    new { Id = 3, Flagged = false },
    new { Id = 4, Flagged = true },
    new { Id = 5, Flagged = false },
    new { Id = 6, Flagged = false },
    new { Id = 7, Flagged = false },
    new { Id = 8, Flagged = true },
    new { Id = 9, Flagged = false }
};

var partitioned = PartitionData(arrayOfElements, x => x.Flagged);

Answer 5

我认为LINQ不适合这个。可以使用Aggregate（）来完成它，但我认为你最好只使用foreach（）来构建结果。

使用Linq将数据分区为数组

5 个答案: