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As you can see in Figure 1, concatenating strings using StringBuilder is much faster, consumes much less memory, and uses fewer garbage collections in all generations, compared to using the '+' operator to combine two or more strings.
Each time strcat calls, the loop will run from start to finish; the longer the string, the longer the loop runs. Until the string is extensive, the string addition takes place very heavy and slow.
Long answer: if you already have an array of strings to concatenate together (with a delimiter), String. Join is the fastest way of doing it. String. Join can look through all of the strings to work out the exact length it needs, then go again and copy all the data.
Update - for those of a facetious frame of mind, you can assume that Aggregate still produces the normal result whatever function is passed to it, including in the case being optimized.
I wrote this program to build a long string of integers from 0 to 19999 separate by commas.
using System;
using System.Linq;
using System.Diagnostics;
namespace ConsoleApplication5
{
class Program
{
static void Main(string[] args)
{
const int size = 20000;
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
Enumerable.Range(0, size).Select(n => n.ToString()).Aggregate((a, b) => a + ", " + b);
stopwatch.Stop();
Console.WriteLine(stopwatch.ElapsedMilliseconds + "ms");
}
}
}
When I run it, it says:
5116ms
Over five seconds, terrible. Of course it's because the whole string is being copied each time around the loop.
But what if make one very small change indicated by the comment?
using System;
using System.Linq;
using System.Diagnostics;
namespace ConsoleApplication5
{
using MakeAggregateGoFaster; // <---- inserted this
class Program
{
static void Main(string[] args)
{
const int size = 20000;
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
Enumerable.Range(0, size).Select(n => n.ToString()).Aggregate((a, b) => a + ", " + b);
stopwatch.Stop();
Console.WriteLine(stopwatch.ElapsedMilliseconds + "ms");
}
}
}
Now when I run it, it says:
42ms
Over 100x faster.
What's in the MakeAggregateGoFaster namespace?
Update 2: Wrote up my answer here.
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