Question

From the following simulation

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;
 }
);

I want to terminate the Aggregation when the balance is less than the withdrawal.But my code travels the entire array.How to terminate it?

Answer 1

It seems to me that you want an Accumulate method which yields a new sequence of accumulated values, instead of a scalar. Something like this:

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;
    }
}

Then you could apply 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);

I could have sworn there was something like this in normal LINQ to Objects, but I can’t find it at the moment…