是否有任何方法可以将List<SomeObject>分离为SomeObject的几个单独的列表，使用项目索引作为每个分割的分隔符?
让我举个例子:
我有一个List<SomeObject>，我需要一个List<List<SomeObject>>或List<SomeObject>[]，这样每个结果列表将包含一组原始列表的3个项目(依次)。
eg.:
原始列表:[a, g, e, w, p, s, q, f, x, y, i, m, c] 结果列表:[a、g e], [w、p, s], [q, f, x]、[y,我,m], [c]
我还需要结果列表的大小是这个函数的参数。
当前回答
这个怎么样?
var input = new List<string> { "a", "g", "e", "w", "p", "s", "q", "f", "x", "y", "i", "m", "c" };
var k = 3
var res = Enumerable.Range(0, (input.Count - 1) / k + 1)
.Select(i => input.GetRange(i * k, Math.Min(k, input.Count - i * k)))
.ToList();
据我所知，GetRange()与所获取的项目数量是线性的。所以这应该表现得很好。
其他回答
我们发现David B的解决方案效果最好。但我们把它改成了一个更普遍的解决方案:
list.GroupBy(item => item.SomeProperty)
.Select(group => new List<T>(group))
.ToArray();
试试下面的代码。
public static List<List<T>> Split<T>(IList<T> source)
{
return source
.Select((x, i) => new { Index = i, Value = x })
.GroupBy(x => x.Index / 3)
.Select(x => x.Select(v => v.Value).ToList())
.ToList();
}
其思想是首先根据索引对元素进行分组。除以3的效果是把它们分成3组。然后将每个组转换为一个列表，将list的IEnumerable转换为list的list
好吧，以下是我的看法:
完全懒惰:工作在无限枚举上 没有中间复制/缓冲 O(n)执行时间 当内部序列仅被部分消耗时也适用
public static IEnumerable<IEnumerable<T>> Chunks<T>(this IEnumerable<T> enumerable, int chunkSize) { if (chunkSize < 1) throw new ArgumentException("chunkSize must be positive"); using (var e = enumerable.GetEnumerator()) while (e.MoveNext()) { var remaining = chunkSize; // elements remaining in the current chunk var innerMoveNext = new Func<bool>(() => --remaining > 0 && e.MoveNext()); yield return e.GetChunk(innerMoveNext); while (innerMoveNext()) {/* discard elements skipped by inner iterator */} } } private static IEnumerable<T> GetChunk<T>(this IEnumerator<T> e, Func<bool> innerMoveNext) { do yield return e.Current; while (innerMoveNext()); } Example Usage var src = new [] {1, 2, 3, 4, 5, 6}; var c3 = src.Chunks(3); // {{1, 2, 3}, {4, 5, 6}}; var c4 = src.Chunks(4); // {{1, 2, 3, 4}, {5, 6}}; var sum = c3.Select(c => c.Sum()); // {6, 15} var count = c3.Count(); // 2 var take2 = c3.Select(c => c.Take(2)); // {{1, 2}, {4, 5}} Explanations The code works by nesting two yield based iterators. The outer iterator must keep track of how many elements have been effectively consumed by the inner (chunk) iterator. This is done by closing over remaining with innerMoveNext(). Unconsumed elements of a chunk are discarded before the next chunk is yielded by the outer iterator. This is necessary because otherwise you get inconsistent results, when the inner enumerables are not (completely) consumed (e.g. c3.Count() would return 6). Note: The answer has been updated to address the shortcomings pointed out by @aolszowka.
看看这个!我有一个序列计数器和日期的元素列表。每次序列重新启动时，我都想创建一个新列表。
例:消息列表。
List<dynamic> messages = new List<dynamic>
{
new { FcntUp = 101, CommTimestamp = "2019-01-01 00:00:01" },
new { FcntUp = 102, CommTimestamp = "2019-01-01 00:00:02" },
new { FcntUp = 103, CommTimestamp = "2019-01-01 00:00:03" },
//restart of sequence
new { FcntUp = 1, CommTimestamp = "2019-01-01 00:00:04" },
new { FcntUp = 2, CommTimestamp = "2019-01-01 00:00:05" },
new { FcntUp = 3, CommTimestamp = "2019-01-01 00:00:06" },
//restart of sequence
new { FcntUp = 1, CommTimestamp = "2019-01-01 00:00:07" },
new { FcntUp = 2, CommTimestamp = "2019-01-01 00:00:08" },
new { FcntUp = 3, CommTimestamp = "2019-01-01 00:00:09" }
};
我想在计数器重新启动时将列表拆分为单独的列表。代码如下:
var arraylist = new List<List<dynamic>>();
List<dynamic> messages = new List<dynamic>
{
new { FcntUp = 101, CommTimestamp = "2019-01-01 00:00:01" },
new { FcntUp = 102, CommTimestamp = "2019-01-01 00:00:02" },
new { FcntUp = 103, CommTimestamp = "2019-01-01 00:00:03" },
//restart of sequence
new { FcntUp = 1, CommTimestamp = "2019-01-01 00:00:04" },
new { FcntUp = 2, CommTimestamp = "2019-01-01 00:00:05" },
new { FcntUp = 3, CommTimestamp = "2019-01-01 00:00:06" },
//restart of sequence
new { FcntUp = 1, CommTimestamp = "2019-01-01 00:00:07" },
new { FcntUp = 2, CommTimestamp = "2019-01-01 00:00:08" },
new { FcntUp = 3, CommTimestamp = "2019-01-01 00:00:09" }
};
//group by FcntUp and CommTimestamp
var query = messages.GroupBy(x => new { x.FcntUp, x.CommTimestamp });
//declare the current item
dynamic currentItem = null;
//declare the list of ranges
List<dynamic> range = null;
//loop through the sorted list
foreach (var item in query)
{
//check if start of new range
if (currentItem == null || item.Key.FcntUp < currentItem.Key.FcntUp)
{
//create a new list if the FcntUp starts on a new range
range = new List<dynamic>();
//add the list to the parent list
arraylist.Add(range);
}
//add the item to the sublist
range.Add(item);
//set the current item
currentItem = item;
}
这个怎么样?
var input = new List<string> { "a", "g", "e", "w", "p", "s", "q", "f", "x", "y", "i", "m", "c" };
var k = 3
var res = Enumerable.Range(0, (input.Count - 1) / k + 1)
.Select(i => input.GetRange(i * k, Math.Min(k, input.Count - i * k)))
.ToList();
据我所知，GetRange()与所获取的项目数量是线性的。所以这应该表现得很好。
