我想構(gòu)建一個流暢的 api 來迭代一個數(shù)組，在這個數(shù)組中我過濾值并繼續(xù)處理剩余的（不是過濾的）值。像這樣的偽代碼：int[] input = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };from a in Take(3) // a = {5,4,1}from b in Skip(4) // b = nullfrom c in TakeWhile(x=> x != 0) // c = {7, 2}select new Stuff(a, b, c)我不知道從哪里開始尋找，這樣的事情的基礎(chǔ)是什么。所以我想尋求一些幫助。系統(tǒng)不應(yīng)該局限于 int 數(shù)字..另一個例子：string[] input = { "how", "are", "you", "doing", "?" };from a in OneOf("how", "what", "where") // a = "how"from b in Match("are") // b = "are"from c in TakeWhile(x=> x != "?") // c = { "you", "doing" }select new Stuff(a, b, c)
1 回答
紅顏莎娜
TA貢獻(xiàn)1842條經(jīng)驗 獲得超13個贊
以下代碼將允許您獲取input.FirstTake(3).ThenSkip(4).ThenTakeWhile(x => x != 0);序列 5、4、1、7、2。主要思想是您需要跟蹤您想要執(zhí)行的拍攝和跳過，以便在您迭代時應(yīng)用它們。這類似于如何OrderBy工作ThenBy。請注意，您不能在兩者之間執(zhí)行其他 Linq 操作。這構(gòu)建了一個連續(xù)跳過和獲取的枚舉，然后該序列將通過您執(zhí)行的任何 Linq 操作提供。
public interface ITakeAndSkip<out T> : IEnumerable<T>
{
ITakeAndSkip<T> ThenSkip(int number);
ITakeAndSkip<T> ThenTake(int number);
ITakeAndSkip<T> ThenTakeWhile(Func<T, bool> predicate);
ITakeAndSkip<T> ThenSkipWhile(Func<T, bool> predicate);
}
public class TakeAndSkip<T> : ITakeAndSkip<T>
{
private readonly IEnumerable<T> _source;
private class TakeOrSkipOperation
{
public bool IsSkip { get; private set; }
public Func<T, bool> Predicate { get; private set; }
public int Number { get; private set; }
private TakeOrSkipOperation()
{
}
public static TakeOrSkipOperation Skip(int number)
{
return new TakeOrSkipOperation
{
IsSkip = true,
Number = number
};
}
public static TakeOrSkipOperation Take(int number)
{
return new TakeOrSkipOperation
{
Number = number
};
}
public static TakeOrSkipOperation SkipWhile(Func<T, bool> predicate)
{
return new TakeOrSkipOperation
{
IsSkip = true,
Predicate = predicate
};
}
public static TakeOrSkipOperation TakeWhile(Func<T, bool> predicate)
{
return new TakeOrSkipOperation
{
Predicate = predicate
};
}
}
private readonly List<TakeOrSkipOperation> _operations = new List<TakeOrSkipOperation>();
public TakeAndSkip(IEnumerable<T> source)
{
_source = source;
}
public IEnumerator<T> GetEnumerator()
{
using (var enumerator = _source.GetEnumerator())
{
// move to the first item and if there are none just return
if (!enumerator.MoveNext()) yield break;
// Then apply all the skip and take operations
foreach (var operation in _operations)
{
int n = operation.Number;
// If we are not dealing with a while then make the predicate count
// down the number to zero.
var predicate = operation.Predicate ?? (x => n-- > 0);
// Iterate the items until there are no more or the predicate is false
bool more = true;
while (more && predicate(enumerator.Current))
{
// If this is a Take then yield the current item.
if (!operation.IsSkip) yield return enumerator.Current;
more = enumerator.MoveNext();
}
// If there are no more items return
if (!more) yield break;
}
// Now we need to decide what to do with the rest of the items.
// If there are no operations or the last one was a skip then
// return the remaining items
if (_operations.Count == 0 || _operations.Last().IsSkip)
{
do
{
yield return enumerator.Current;
} while (enumerator.MoveNext());
}
// Otherwise the last operation was a take and we're done.
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public ITakeAndSkip<T> ThenSkip(int number)
{
_operations.Add(TakeOrSkipOperation.Skip(number));
return this;
}
public ITakeAndSkip<T> ThenSkipWhile(Func<T, bool> predicate)
{
_operations.Add(TakeOrSkipOperation.SkipWhile(predicate));
return this;
}
public ITakeAndSkip<T> ThenTake(int number)
{
_operations.Add(TakeOrSkipOperation.Take(number));
return this;
}
public ITakeAndSkip<T> ThenTakeWhile(Func<T, bool> predicate)
{
_operations.Add(TakeOrSkipOperation.TakeWhile(predicate));
return this;
}
}
public static class TakeAndSkipExtensions
{
public static ITakeAndSkip<T> FirstTake<T>(this IEnumerable<T> source, int number)
{
return new TakeAndSkip<T>(source).ThenTake(number);
}
public static ITakeAndSkip<T> FirstSkip<T>(this IEnumerable<T> source, int number)
{
return new TakeAndSkip<T>(source).ThenSkip(number);
}
public static ITakeAndSkip<T> FirstTakeWhile<T>(this IEnumerable<T> source, Func<T, bool> predicate)
{
return new TakeAndSkip<T>(source).ThenTakeWhile(predicate);
}
public static ITakeAndSkip<T> FirstSkipWhile<T>(this IEnumerable<T> source, Func<T, bool> predicate)
{
return new TakeAndSkip<T>(source).ThenSkipWhile(predicate);
}
}
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