Linq效率问题 - foreach与聚合

Question

哪个更有效率？

//Option 1
foreach (var q in baseQuery)
{
  m_TotalCashDeposit += q.deposit.Cash
  m_TotalCheckDeposit += q.deposit.Check
  m_TotalCashWithdrawal += q.withdraw.Cash
  m_TotalCheckWithdrawal += q.withdraw.Check
}

//Option 2
m_TotalCashDeposit = baseQuery.Sum(q => q.deposit.Cash);
m_TotalCheckDeposit = baseQuery.Sum(q => q.deposit.Check);
m_TotalCashWithdrawal = baseQuery.Sum(q => q.withdraw.Cash);
m_TotalCheckWithdrawal = baseQuery.Sum(q => q.withdraw.Check);

我想我要问的是,调用Sum将基本列举在列表上吗？所以,如果我四次打电话给Sum,是不是列举了四次列表呢？只做一个foreach不是更有效率所以我只需要列举一次列表吗？

Answer 1

它可能,也可能不是,它取决于.

唯一确定的方法是实际测量它.

测量它的简单代码:

void Main()
{
    BenchmarkSwitcher.FromAssembly(GetType().Assembly).RunAll();
}

public class Benchmarks
{
    [Benchmark]
    public void Option1()
    {
//        foreach (var q in baseQuery)
//        {
//            m_TotalCashDeposit += q.deposit.Cash;
//            m_TotalCheckDeposit += q.deposit.Check;
//            m_TotalCashWithdrawal += q.withdraw.Cash;
//            m_TotalCheckWithdrawal += q.withdraw.Check;
//        }
    }

    [Benchmark]
    public void Option2()
    {
//        m_TotalCashDeposit = baseQuery.Sum(q => q.deposit.Cash);
//        m_TotalCheckDeposit = baseQuery.Sum(q => q.deposit.Check);
//        m_TotalCashWithdrawal = baseQuery.Sum(q => q.withdraw.Cash);
//        m_TotalCheckWithdrawal = baseQuery.Sum(q => q.withdraw.Check);
    }
}

您应该多次运行代码以避免JITting对您的计时产生太大的影响.