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.
Part 1 We create a List of strings by invoking the List constructor, and then calling Add() 3 times.
Part 2 We use the string.Join method to combine a List of strings into one string. The output can be used as a CSV record.
Info In previous versions of .NET, we had to call ToArray on a List before using Join. In older programs this is still required.
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.
And Append() will handle the int on its own. It will convert it to a string and append it.
Detail StringBuilder is fast for most programs. More speed could be acquired by using a char[] and then converting to a string.
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.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Dec 15, 2021 (edit).
