Question

来自以下模拟

int[] amountWithdrawal = { 10, 20, 30, 140, 50, 70 };

amountWithdrawal.Aggregate(100, (balance, withdrawal) => 
{
  Console.WriteLine("balance :{0},Withdrawal:{1}", balance, withdrawal);
 if (balance >= withdrawal)
 {
   return balance - withdrawal;
 }
 else return balance;
 }
);

我想终止聚合when the balance is less than the withdrawal。但我的代码遍历整个数组。如何终止它？

Answer 1

在我看来，你想要一个Accumulate方法，它产生一个新的累积值序列，而不是标量。像这样：

public static IEnumerable<TAccumulate> SequenceAggregate<TSource, TAccumulate>(
    this IEnumerable<TSource> source,
    TAccumulate seed,
    Func<TAccumulate, TSource, TAccumulate> func)
{
    TAccumulate current = seed;
    foreach (TSource item in source)
    {
        current = func(current, item);
        yield return current;
    }
}

然后你可以申请TakeWhile：

int[] amountWithdrawal = { 10, 20, 30, 140, 50, 70 };

var query = amountWithdrawal.SequenceAggregate(100, (balance, withdrawal) => 
{
  Console.WriteLine("balance :{0},Withdrawal:{1}", balance, withdrawal);
  return balance - withdrawal;
}).TakeWhile (balance => balance >= 0);

我可以发誓在正常的LINQ to Objects中有类似的东西，但我现在找不到它......

Answer 2

您应该照常使用Aggregate，然后使用Where省略负余额。

BTW，在LINQ方法中使用带副作用的函数（例如Console.WriteLine）是不好的做法。你最好先做所有的LINQ聚合和过滤，然后写一个foreach循环打印到控制台。

Answer 3

用for循环替换聚合。

Answer 4

您可能希望使用TakeWhile().Aggregate()并检查take while谓词中的余额。

C＃ - 聚合中的终止（）

4 个答案: