使用LINQ的多个SUM [英] Multiple SUM using LINQ

问题描述

我有如下循环，我可以使用多个SUM来做同样的事情吗?

I have a loop like the following, can I do the same using multiple SUM?

foreach (var detail in ArticleLedgerEntries.Where(pd => pd.LedgerEntryType == LedgerEntryTypeTypes.Unload &&
                                                                pd.InventoryType == InventoryTypes.Finished))
{
     weight += detail.GrossWeight;
     length += detail.Length;
     items  += detail.NrDistaff;
}

推荐答案

从技术上讲，您拥有的可能是最有效的方式来完成您要问的事情.但是，您可以在IEnumerable< T>上创建扩展方法.称为Each可能会使它更简单:

Technically speaking, what you have is probably the most efficient way to do what you are asking. However, you could create an extension method on IEnumerable<T> called Each that might make it simpler:

public static class EnumerableExtensions
{
    public static void Each<T>(this IEnumerable<T> col, Action<T> itemWorker)
    {
        foreach (var item in col)
        {
            itemWorker(item);
        }
    }
}

并这样称呼它:

// Declare variables in parent scope
double weight;
double length;
int items;

ArticleLedgerEntries
    .Where(
        pd => 
           pd.LedgerEntryType == LedgerEntryTypeTypes.Unload &&
           pd.InventoryType == InventoryTypes.Finished
    )
    .Each(
        pd => 
        {
            // Close around variables defined in parent scope
            weight += pd.GrossWeight; 
            lenght += pd.Length;
            items += pd.NrDistaff;
        }
    );

更新: 只是另外一注.上面的示例依赖于闭包.应在父作用域中声明变量weight，length和items，以允许它们在对itemWorker操作的每次调用之后都可以持续存在.为了清楚起见，我已经更新了示例以反映这一点.

UPDATE: Just one additional note. The above example relies on a closure. The variables weight, length, and items should be declared in a parent scope, allowing them to persist beyond each call to the itemWorker action. I've updated the example to reflect this for clarity sake.

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