Concat all strings from dictionary (values) using LINQ without external variable

Question

Having dictionary where key can be anything (e.g. int) and values is some text I want to output.

Dictionary<int, string> dict = new Dictionary<int, string>();

dict.Add(1, "This is the first line.");
dict.Add(2, "This is the second line.");
dict.Add(3, "This is the third line.");

To get output:

string lResult = dict. ... //there should go the LINQ query
Console.WriteLine(lResult);

Output:

This is the first line.
This is the second line.
This is the third line.

Q: Is it possible to concatenate the lines from Dictionary to have them as one string without using external variable?

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I tried approach using some Select/SelectMany/Zip solutions, but I cannot figure how to pass the value from 1 LINQ call to other without using external variable.

Another idea is to Select values, put them to the List and then Concatenate (again using external variable). Like:

string tmp = "";
dict.Select(a => a.Value).ToList().ForEach(b => tmp += b);

Answer 1

You shouldn't use LINQ to concat strings. This can become very expenisve. Use string.Join() innstead:

string result = string.Join(Environment.NewLine, dict.Values);

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However, this does not guarantee the correct order, because a Dictionary<> is not sorted. To sort the output by the Keys you can do this:

string sorted = string.Join(Environment.NewLine, 
                     dict.OrderBy(kvp => kvp.Key).Select(kvp => kvp.Value));

Answer 2

You can do:

string.Join(Environment.NewLine, dict.Values)

Note however, that the documentation states the values will be retrieved in an unspecified order.

Answer 3

I suggest using StringBuilder if you want to use LINQ. Otherwise the performance will suffer too much:

string lResult = dict.Values.Aggregate(new StringBuilder(), (a, b) => a.Append(b)).ToString()

Answer 4

Appending string in a loop

ForEach(b => tmp += b)

is an antipattern; you should use StringBuilder. In case you have to use Linq (not string.Join which is specially designed for it):

  dict.Add(1, "This is the first line.");
  dict.Add(2, "This is the second line.");
  dict.Add(3, "This is the third line.");

  string result = dict
    .OrderBy(pair => pair.Key)
    .Aggregate((StringBuilder) null, 
               (sb, pair) => (sb == null 
                  ? new StringBuilder() 
                  : sb.Append(Environment.NewLine)).Append(pair.Value))
    .ToString();