Collections are one of the most commonly used types in programming. For any program that uses data, you will be dealing with collections. One of the most common things we do is to iterate over the collection to process the data. There are three main ways to iterate over a collection in .NET…
For
For is a common statement in many programming languages by using a counter variable to iterate over a collection.
for (int personCount = 0; personCount < _personCollection.Count - 1; personCount++)
{
var name = _personCollection[personCount].FirstName;
}
Foreach
Foreach was the statement I usually used because it’s cleaner and easier to read.
foreach (var person in _personCollection)
{
var name = person.FirstName;
}
Foreach with AsParallel()
Parallel () is part of LINQ and could increase performance if there is a significant load with processing the data.
foreach (var person in _personCollection.AsParallel())
{
var name = person.FirstName;
}
Performance
I’ve done a lot of benchmarking using for, foreach, and foreachAsParallel() for my book on code performance. I ran the benchmark four times using a collection count of 100, 500, 2000, and 5000. Included in this test is the comparison between .NET Clr 4.7.2 and .NET Core 2.2. Below are the results.
| Test |
Runtime |
Collection Count |
Mean (ns) |
LR vs CORE Difference |
| for |
Clr 4.7.2 |
100 |
108.8216 |
|
| foreach |
Clr 4.7.2 |
100 |
308.1016 |
|
| foreach AsParallel() |
Clr 4.7.2 |
100 |
853.7294 |
|
| for |
Core 2.2 |
100 |
108.3985 |
-0.4231 |
| foreach |
Core 2.2 |
100 |
334.339 |
26.2374 |
| foreach AsParallel() |
Core 2.2 |
100 |
821.127 |
-32.60 |
| for |
Clr 4.7.2 |
500 |
672.2033 |
|
| for each |
Clr 4.7.2 |
500 |
1,619.09 |
|
| foreach AsParallel() |
Clr 4.7.2 |
500 |
3,881.51 |
|
| for |
Core 2.2 |
500 |
671.033 |
-1.17 |
| foreach |
Core 2.2 |
500 |
1,662.23 |
43.14 |
| foreach AsParallel() |
Core 2.2 |
500 |
3,626.62 |
-254.89 |
| for |
Clr 4.7.2 |
2000 |
3,400.98 |
|
| foreach |
Clr 4.7.2 |
2000 |
7,615.78 |
|
| foreach AsParallel() |
Clr 4.7.2 |
2000 |
18,726.19 |
|
| for |
Core 2.2 |
2000 |
3,422.70 |
21.72 |
| foreach |
Core 2.2 |
2000 |
7,444.41 |
-171.36 |
| foreach AsParallel() |
Core 2.2 |
2000 |
13,814.03 |
-4,912.16 |
| for |
Clr 4.7.2 |
5000 |
10,242.85 |
|
| foreach |
Clr 4.7.2 |
5000 |
21,524.22 |
|
| foreach AsParallel() |
Clr 4.7.2 |
5000 |
38,018.76 |
|
| for |
Core 2.2 |
5000 |
10,330.39 |
87.54 |
| foreach |
Core 2.2 |
5000 |
21,290.93 |
-233.29 |
| foreach AsParallel() |
Core 2.2 |
5000 |
35,289.98 |
-2,728.78 |
The test was done using a business object called Person to mimic a real-world object. As you can see, using for is around 2-3 times faster than for each! Wow, I was surprised when I first saw this. The benchmark comparing the .NET Clr 4.7.2 to .NET Core 3 produced similar results.
In most tests, .NET Core is faster than the Clr. Moving to .NET Core should be on your team’s roadmap if you aren’t already moving to it.
Summary
My recommendation is to always use for and avoid for each. I would also avoid using foreach with AsParallel() unless there is a load during the processing of the data. In all my open-source projects and any code that I work on in my contracts, I am always using for from now on.
Do you have any performance tips when using collections? Please make a comment below.