using LINQ in C# to convert a List<string> to a List<char>

Question

I have a list of strings in C#, and want to create a list of unique characters that are in the strings in the list, using LINQ.

I have so far worked out how to turn the List into a List, but I can't work out how to get the LINQ to go further than that.

What I have so far is as follows:

List<string> dictionary = new List<string>(someArray);
List<string[]> uniqueCharacters = dictionary.ConvertAll(s => s.Split());

I believe I need to something along the lines of

List<char> uniqueCharacters =
     dictionary.ConvertAll(s => s.Split()).SelectAll(t, i=>t[i][0]);

Matthew Abbott · Accepted Answer · 2010-07-02 07:49:58Z

16

You can use LINQ's SelectMany method, e.g.:

var list = new List<string> { "Foo", "Bar" };

var chars = list.SelectMany(s => s.ToCharArray());
var distinct = chars.Distinct();

answered Jul 2, 2010 at 7:49

Matthew Abbott

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3 Comments

simonalexander2005 Over a year ago

List<char> uniqueCharacters = dictionary.SelectMany(s => s.ToCharArray()).Distinct().ToList(); is what I went with in the end - thanks :)

Ian Mercer Over a year ago

Using a HashSet at the end var distinct = new HashSet(chars) is another reasonable alternative if the question is interpreted more liberally. See also stackoverflow.com/questions/1388361/…

LukeH Over a year ago

The ToCharArray call is unnecessary and has a small impact on performance because the characters need to be copied from the source string to a new array. You can just do list.SelectMany(s => s) instead.

Serkan Hekimoglu · Accepted Answer · 2010-07-02 07:45:57Z

1

Get your LinQ result and put it in loop, compare every char with in list of char.

foreach (string character in dictionary)
        {
            if (!(uniqueCharacters).Contains(character))
            {
                uniqueCharacters.Add(character);
            }
        }

answered Jul 2, 2010 at 7:45

Serkan Hekimoglu

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2 Comments

simonalexander2005 Over a year ago

Good answer, but I was hoping to be able to do it all in LinQ - for the learning experience, if nothing else

Serkan Hekimoglu Over a year ago

Its just like an Sql command DISTINCT write your LinQ Query, and add Distinct() at last

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