通过列表值获取字典键

Question

I'll take inspiration from this previous question . I have a dictionary with lists inside, and I want to get the key by a value inside one of those.

Dictionary<string, List<string>> myDict = new Dictionary<string, List<string>>
{
    {"1", new List<string>{"1a", "1b"} },
    {"2", new List<string>{"2a", "2b"} },
    {"3", new List<string>{"3a", "3b"} },
};

I'm confident that all values inside are unique.

I want something like this:

getByValueKey(string value);

getByValueKey("2a") must be return "2".

Answer 1

if you want to use linq, you could write:

var result = myDict.FirstOrDefault(p => p.Value.Contains(stringTofind)).Key;

Answer 2

I like Frenchy's answer, but if you're looking for a non-linqy solution, then:

Dictionary<string, List<string>> myDict = new Dictionary<string, List<string>>
{
    {"1", new List<string>{"1a", "1b"} },
    {"2", new List<string>{"2a", "2b"} },
    {"3", new List<string>{"3a", "3b"} },
};

string stringToFind = "2a";

string matchingKey = null;
foreach(KeyValuePair<string, List<string>> kvp in myDict)
{
    if (kvp.Value.Contains(stringToFind))
    {
        matchingKey = kvp.Key;
        break;
    }
}

if (matchingKey != null)
{
    System.Console.WriteLine("Matching Key: " + matchingKey);
}
else
{
    System.Console.WriteLine("No match found.");
}