Convert List, string

Think of a sentence. It contains some words. We could represent a sentence as a single string—one with spaces. But a list of strings (of words) is sometimes better.

We can convert our string into a List of smaller strings. For the reverse, we can convert our List into a string. A List can be joined directly as it is an IEnumerable type.

First example

Often the best way to convert a List of strings into an array is the string.Join method. This is built into the .NET Framework, so we do not need to write any custom code.

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Part 1: create list of strings.
        List<string> animals = new List<string>();
        animals.Add("bird");
        animals.Add("bee");
        animals.Add("cat");

        // Part 2: use string.Join and pass the list as an argument.
        string result = string.Join(",", animals);
        Console.WriteLine($"RESULT: {result}");
    }
}
RESULT: bird,bee,cat

StringBuilder

Here we use the StringBuilder class to convert a List to a single string. We can convert a List of any object type into a string this way.

using System;
using System.Collections.Generic;
using System.Text;

class Program
{
    static void Main()
    {
        List<string> cats = new List<string>();
        cats.Add("Devon Rex");
        cats.Add("Manx");
        cats.Add("Munchkin");
        cats.Add("American Curl");
        cats.Add("German Rex");

        StringBuilder builder = new StringBuilder();
        // Loop through all strings.
        foreach (string cat in cats)
        {
            // Append string to StringBuilder.
            builder.Append(cat).Append("|");
        }
        // Get string from StringBuilder.
        string result = builder.ToString();
        Console.WriteLine(result);
    }
}
Devon Rex|Manx|Munchkin|American Curl|German Rex|

Int List

Here we convert a List of ints into a single string. The StringBuilder's Append method receives a variety of types. We can simply pass it the int.

using System;
using System.Collections.Generic;
using System.Text;

class Program
{
    static void Main()
    {
        List<int> safePrimes = new List<int>();
        safePrimes.Add(5);
        safePrimes.Add(7);
        safePrimes.Add(11);
        safePrimes.Add(23);

        StringBuilder builder = new StringBuilder();
        foreach (int safePrime in safePrimes)
        {
            // Append each int to the StringBuilder overload.
            builder.Append(safePrime).Append(" ");
        }
        string result = builder.ToString();
        Console.WriteLine(result);
    }
}
5 7 11 23

CSV string

Finally, we get a List of strings from a string in CSV format. This requires the Split method. If you require per-item conversion, loop over the string array returned by Split.

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        string csv = "one,two,three";
        string[] parts = csv.Split(',');
        // Use List constructor.
        List<string> list = new List<string>(parts);
        foreach (string item in list)
        {
            Console.WriteLine(item);
        }
    }
}
one
two
three

A summary

We converted Lists and strings using the string.Join methods and the StringBuilder approach. The List is easily concatenated and stored in a database or file with these methods.