C# 根据列表的不同值迭代列表的有效方法是什么？

在上面的代码片段中，skuStoreStockLevels恰好是一个类型为Tuple的列表，Item1是StoreID。得到一个不同的列表后，它会遍历（非不同的）列表以获得每个适用的项。效率低下的是（大的）内部列表对于每个不同的项目（StoreID）重复迭代。

更新：纯LINQ解决方案。这将为您提供为每组项目创建的字符串列表

string sStoreStockFeed = "";
string sSeparator = "";

var distinctStoreIDList = skuStoreStockLevels.Select(x => x.Item1).Distinct();

    foreach (var storeID in distinctStoreIDList)
    {
        foreach (var item in skuStoreStockLevels)
        {
            if (item.Item1 == storeID)
            {
               // add this one to a job for this store
                       sStoreStockFeed += sSeparator + item.Item1.ToString() + "," + item.Item2.ToString() + "," + item.Item3.ToString();
                       sSeparator = "|";
            }
        }
      // some code to process the string before moving on
      sStoreStockFeed = "";
      sSeparator = "";
    }

另外还有其他选项-顺序排序。相等的项目将依次出现

var query = skuStoreStockLevel.GroupBy(x => x.Item1)
                .Select(g => g.Aggregate(new StringBuilder(),
                                         (sb, x) => sb.AppendFormat("{0}{1},{2},{3}", sSeparator, x.Item1, x.Item2, x.Item3),
                                         (sb) => sb.ToString()));

foreach(var feed in query)
    // some code to process the string before moving on

或者您可以使用分组

int storeID = -1;
StringBuilder builder = new StringBuilder();

foreach (var item in skuStoreStockLevel.OrderBy(x => x.Item1))
{
    builder.AppendFormat("{0}{1},{2},{3}", sSeparator, item.Item1, item.Item2, item.Item3);
    if (item.Item1 != storeID)
    {
        // some code to process the string before moving on
        storeID = item.Item1;
    }       
}

---

当然，最好使用

StringBuilder

来创建字符串。

更新：纯LINQ解决方案。这将为您提供为每组项目创建的字符串列表

string sStoreStockFeed = "";
string sSeparator = "";

var distinctStoreIDList = skuStoreStockLevels.Select(x => x.Item1).Distinct();

    foreach (var storeID in distinctStoreIDList)
    {
        foreach (var item in skuStoreStockLevels)
        {
            if (item.Item1 == storeID)
            {
               // add this one to a job for this store
                       sStoreStockFeed += sSeparator + item.Item1.ToString() + "," + item.Item2.ToString() + "," + item.Item3.ToString();
                       sSeparator = "|";
            }
        }
      // some code to process the string before moving on
      sStoreStockFeed = "";
      sSeparator = "";
    }

另外还有其他选项-顺序排序。相等的项目将依次出现

var query = skuStoreStockLevel.GroupBy(x => x.Item1)
                .Select(g => g.Aggregate(new StringBuilder(),
                                         (sb, x) => sb.AppendFormat("{0}{1},{2},{3}", sSeparator, x.Item1, x.Item2, x.Item3),
                                         (sb) => sb.ToString()));

foreach(var feed in query)
    // some code to process the string before moving on

或者您可以使用分组

int storeID = -1;
StringBuilder builder = new StringBuilder();

foreach (var item in skuStoreStockLevel.OrderBy(x => x.Item1))
{
    builder.AppendFormat("{0}{1},{2},{3}", sSeparator, item.Item1, item.Item2, item.Item3);
    if (item.Item1 != storeID)
    {
        // some code to process the string before moving on
        storeID = item.Item1;
    }       
}

当然，最好使用

StringBuilder

来创建字符串。

使用Linq，它将为您构建一个分组项目列表：

StringBuilder builder = new StringBuilder();

foreach (var storeGroup in skuStoreStockLevel.GroupBy(x => x.Item1))
{
    foreach (var item in storeGroup)
          builder.AppendFormat("{0}{1},{2},{3}", sSeparator, item.Item1, item.Item2, item.Item3);        

    // some code to process the string before moving on
}

使用Linq将为您生成一个分组项目列表：

StringBuilder builder = new StringBuilder();

foreach (var storeGroup in skuStoreStockLevel.GroupBy(x => x.Item1))
{
    foreach (var item in storeGroup)
          builder.AppendFormat("{0}{1},{2},{3}", sSeparator, item.Item1, item.Item2, item.Item3);        

    // some code to process the string before moving on
}

---

制作一个映射

storeID->job

，并在列表中迭代一次。如果

storeID

尚未在地图中，请将其与新作业一起添加。否则，为其

storeID

，将存储添加到作业中-哦，这看起来很像C#，不是C，所以我重新标记了它。你的助手看起来很奇怪，这是故意的吗。我怀疑以后在sStoreStockFeed中读取结果会非常困难。你可能会得到这样的结果：A，2,3 | A，4,5B，1,2C，3,4 | C，6,7…制作一张地图

storeID->job

，并在列表中迭代一次。如果

storeID

尚未在地图中，请将其与新作业一起添加。否则，为其

storeID

，将存储添加到作业中-哦，这看起来很像C#，不是C，所以我重新标记了它。你的助手看起来很奇怪，这是故意的吗。我怀疑以后在sStoreStockFeed中读取结果会非常困难。你可能会得到这样的结果：A，2，3，A，4，5B，1，2C，3，4，C，6，7。。。