c# - LINQ - 聚合和计算多个参数

Question

我有以下内容

List<Stock> _investments= new List<Stock>()
        {
            new Stock {id=msft, price =12, qty=20}
            new Stock {id=msft, price =53, qty=50}
            new Stock {id=csco, price =222, qty=20}
            new Stock {id=fb, price 40, qty=100}
        }

给定一个符号，比如 msft，我想获得总投资和收取的价格。在上述情况下，它将是

id=msft, qty=70, price = (12*20 + 53 *50)/70 = 41.29

如何在 LINQ 中做到这一点？我可以这样得到 12*20 + 53*50:

var c = _investments.Where(i => i.ID == investmentName.ToUpper()).Sum(k => k.InitialPrice * k.Qty);

但是如何以一种有效的方式包含总数量

Answer 1

最简单的方法似乎是:

var relevantInvestments = _investments
    .Where(i => i.ID == investmentName.ToUpper())
    .ToArray();

var totalQty = relevantInvestments.Sum(k => k.Qty);
var c = relevantInvestments.Sum(k => k.InitialPrice * k.Qty) / totalQty;

只迭代一次:

var c = _investments
    .Where(i => i.ID == investmentName.ToUpper())
    .Aggregate(
        new { Price = 0, TotalQty = 0 },
        (total, i) => new 
                      { 
                          Price = total.Price + i.InitialPrice * i.Qty,
                          TotalQty = total.TotalQty + i.Qty
                      },
        i => i.Price / i.TotalQty);