C# ToDictionary lambda select index and element?

Question

I have a string like string strn = \"abcdefghjiklmnopqrstuvwxyz\" and want a dictionary like:

Dictionary(){
    {\'a\',0},
    {         


        

Answer 1

Use the .Select operator first:

strn
    .Select((x, i) => new { Item = x, Index = i })
    .ToDictionary(x => x.Item, x => x.Index);

Answer 2

You could try something like this:

    string strn = "abcdefghjiklmnopqrstuvwxyz";

Dictionary<char,int> lookup = strn.ToCharArray()
    .Select( ( c, i ) => new KeyValuePair<char,int>( c, i ) )
        .ToDictionary( e => e.Key, e => e.Value );

Answer 3

What am I doing wrong?

You're assuming there is such an overload. Look at Enumerable.ToDictionary - there's no overload which provides the index. You can fake it though via a call to Select:

var dictionary = text.Select((value, index) => new { value, index })
                     .ToDictionary(pair => pair.value,
                                   pair => pair.index);