聚合中的C# -Termination ()

Question

从下面的模拟

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.But我的代码遍历整个array.How来终止它？

Answer 1

在我看来，您需要一个Accumulate方法来生成一个新的累加值序列，而不是一个标量。如下所示：

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，您可以应用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);

我可以发誓在普通的LINQ to Objects中有这样的东西，但我现在找不到了……

Answer 2

您应该像往常一样使用Aggregate，然后使用Where忽略负余额。

顺便说一句，在LINQ方法中使用有副作用的函数(比如Console.WriteLine)是不好的做法。您最好先执行所有的LINQ聚合和过滤，然后编写一个foreach循环以打印到控制台。

Answer 3

用for循环替换aggregate。