字典 <something, List<> &gt;展平（取消分组）到列表中的某物和元素的列表-C＃

Question

I want to flatten (ungroup) my dictionary - and trying if it can be done by Linq.

Sample input:

Dictionary<int, List<string>> dict = new Dictionary<int, System.Collections.Generic.List<string>>();
dict.Add(0, new List<string>() { "a", "b" });
dict.Add(1, new List<string>() { "c", "d"});

What i want to achieve is List of following elements:

0a

0b

1c

1d

of course it can be done with:

List<string> output = new List<string>();
foreach (var element in dict)
{
    foreach (var valuesElement in element.Value)
    {
        output.Add(element.Key + valuesElement);
    }
}

I'm only looking if there is any "clever" linq construction to achieve it.

Answer 1

Use SelectMany on the dictionary and the construct the items based on value in the key value pair

Dictionary<int, List<string>> dict = new Dictionary<int, System.Collections.Generic.List<string>>();
dict.Add(0, new List<string>() { "a", "b" });
dict.Add(1, new List<string>() { "c", "d" });

List<string> output = dict.SelectMany(kvp => kvp.Value.Select(v => string.Format("{0}{1}", kvp.Key, v))).ToList(); 

Answer 2

You are looking for .SelectMany()

dict.SelectMany(x => x.Value.Select(y => $"{x.Key}{y}"));

Here's more explanation on how it works.