Concatenating List<List<string>> takes a long time

Question

What I had tried till Now

string Value ="";
foreach (List<string> val in L1)
{
   Value = Value + string.Join(",", val) + " // ";
}

Where L1 is of datatype List <List<strings>>

This Works, But its take almost n half hour to complete Is there as many fastest and simple way to achieve this.

Answer 1

I'd suggest use StringBuilder instead of concatenations in a loop like that:

StringBuilder builder = new StringBuilder();
foreach (List<string> val in L1)
{
    builder.Append(string.Join(",", val) + " // ");
}
string result = builder.ToString();

When concatenating in a loop it needs to copy the string everytime to a new position in memory with the extra allocated memory. StringBuilder prevents that.

You can also refer to:

• How to use StringBuilder wisely
• How does StringBuilder work?
• How the StringBuilder class is implemented? Does it internally create new string objects each time we append?