Question

I want to get a list of subelements from a subdictionary

I have this:

Dictionary<string, Dictionary<string, List<InstanceLog>>> dic;

And I want something like this (Fetch all InstanceLog-Lists from the subdictinary in one big list.):

List<InstanceLog> logList = GetValues(dic);

I have tried something like this but it don't work:

List<InstanceLog> logList = GetFetchtedList()
  .Select(x => x.Value.ToList())
  .Cast<InstanceLog>()
  .ToList()

Thanks a lot for the help!

Answer 1

您必须展平 dic 两次：

Dictionary<string, Dictionary<string, List<InstanceLog>>> dic = ...;

List<InstanceLog> logList = dic
  .SelectMany(pair => pair.Value) // Inner Dictionaries
  .SelectMany(pair => pair.Value) // Inner Lists
  .ToList();                      // Materialized as one big list

Answer 2

以技术用语，您想拼合存储在字典值中的列表，因此您需要SelectMany：

var values = dic.Values
                 .SelectMany(val => val.Values)
                 .SelectMany(val => val);

其中values将是您所需要的IEnumerable<InstanceLog>类型数据的集合。

Answer 3

SelectMany是关键字。如果选择是某种形式的集合，它将作为一个列表分组。如果您希望它像返回Union一样返回。

Dictionary<string, Dictionary<string, List<InstanceLog>>> dic;

var instanceLogs = dic.SelectMany(d => d.Value.Select(subd => subd.Value)).ToList();

SelectMany上的dic告诉linq：

“嘿，我将在这些括号内找到一个收集结果，因此将它们归为1个收集”

子词典上的Select仅返回集合1，供SelectMany抓取并处理。

此操作仅迭代一次，并且不使用任何不需要的额外操作（明智的选择）

How can I get a List of subelements from a subdictionary?

3 个答案: