C# Get all keys from a list of dictionaries

Question

I basically want to know how to write this (Extract all keys from a list of dictionaries) in C#.

I have a list of dictionaries which have all unique keys.

I want to extract all of them into a list of string (as the key is string).

private List<Dictionary<string, string>> dictList = new List<Dictionary<string, string>>
{
     new Dictionary<string, string>() { { "a", "b" } },
     new Dictionary<string, string>() { { "c", "d" } },
};

private void GetDictListKeys()
{
    List<string> keyList = new List<string>();
    foreach(var dict in dictList)
    {
        keyList.Add(dict.Keys.ToString());
    }
}

Thank you.

score 5 · Accepted Answer · answered Aug 09 '22 at 17:56

5

You want to flatten your enumerable of keys and dump it into a collection (HashSet used cause you mentioned duplicates, and because that's also what your linked answer used in Python):

var allKeys = dictList.SelectMany(d => d.Keys).ToHashSet();

answered Aug 09 '22 at 17:56

Blindy

65,249
10
91
131

If you actually want a list, use `ToList()` instead. – Blindy Aug 09 '22 at 17:56
... or if you want unique keys but a list use `dictList.SelectMany(d => d.Keys).Distinct().ToList()` – Tim Schmelter Aug 09 '22 at 18:11

score 2 · Answer 2 · edited Aug 13 '22 at 19:21

2

You can create another foreach loop inside yours:

foreach (Dictionary<string,string> dict in dictList)
{
    foreach(string key in dict.Keys)
    {
        keyList.Add(key);                 
    }
}

edited Aug 13 '22 at 19:21

josibu

594
1
6
23

answered Aug 09 '22 at 18:01

MTO

41
5

Couldn't really think of having two loops! Thank you very much! – MarcelloWrites Aug 09 '22 at 18:39

score 2 · Answer 3 · answered Aug 09 '22 at 18:05

2

You can use AddRange.

    foreach (var dict in dictList)
    {
        keyList.AddRange(dict.Keys);
    }

answered Aug 09 '22 at 18:05

thewallrus

645
4
8

Another beautiful way to get what I wanted. Thank you! – MarcelloWrites Aug 09 '22 at 18:39

C# Get all keys from a list of dictionaries

3 Answers3