C＃Linq-提取字典中列表的成员

Question

I have a use case for a dictionary like this one

var foo = new Dictionary<string, List<string>>()

so this collection will hold some hierarchical data like this

• Key 1
  • Value 1
  • Value 2
• Key 2
  • Value 3

and I need to get\\project a list of values ignoring the keys, so result would be

• Value 1
• Value 2
• Value 3

on the first attempt I came up with this

IReadOnlyList<string> bar = foo.Select(r => r.Value.Select(x => x.ToString()))
                             .Select(r => r.ToString())
                             .ToList();

Is this any good?

Answer 1

使用SelectMany ：

foo.SelectMany(x => x.Value).ToList();

Answer 2

Note that Dictionary already provides an O(1) way to access its list of values (same as you can access its list of keys) via its Values property

The order of the values in the Dictionary.ValueCollection is unspecified, but it is the same order as the associated keys in the Dictionary.KeyCollection returned by the Keys property.

The returned Dictionary.ValueCollection is not a static copy; instead, the Dictionary.ValueCollection refers back to the values in the original Dictionary. Therefore, changes to the Dictionary continue to be reflected in the Dictionary.ValueCollection.

Getting the value of this property is an O(1) operation.

https://msdn.microsoft.com/en-us/library/ekcfxy3x(v=vs.110).aspx