Liệu thực sự Linq có nhanh hơn vòng lặp for, foreach, while

private long OnStopWatch(Action action)
{
var st = new Stopwatch();
st.Start();
action();
st.Stop();
return st.ElapsedTicks;
}

private void CreateListRandom(int totalNumber, List list1)
{
for (var i = 1; i <= totalNumber; i++)
{
list1.Add(Singleton.Inst.Next(0, 100));
}
}

public void Test1(int totalNumber)
{
if (totalNumber > 50000) throw new Exception("Vui lòng chọn số lượng mảng nhỏ hơn 50000");

var list = new List { };
CreateListRandom(totalNumber, list);

var sumByFor = 0;
var t1 = OnStopWatch(() =>
{
for (var i = 0; i < list.Count; i++) { sumByFor += list[i]; } }); var sumByForEach = 0; var t2 = OnStopWatch(() =>
{
foreach (var item1 in list)
{
sumByForEach += item1;
}
});

var sumByJoinLinq = 0;
var t3 = OnStopWatch(() =>
{
sumByJoinLinq = list.Sum(item => item);
});

this.SetData("Result", new { t1, sumByFor, t2, sumByForEach, t3, sumByJoinLinq, list1 = list.JoinString(item => item, " ") });
}

private void CreateListRandom(int totalNumber, List list1, List list2)
{
for (var i = 1; i <= totalNumber; i++)
{
list1.Add(Singleton.Inst.Next(0, 100));
list2.Add(Singleton.Inst.Next(0, 100));
}
}

public void Test2(int totalNumber)
{
if (totalNumber > 50000) throw new Exception("Vui lòng chọn số lượng mảng nhỏ hơn 50000");

// Tạo 2 mảng ngẫu nhiên
var list1 = new List { };
var list2 = new List { };
CreateListRandom(totalNumber, list1, list2);

var sumByFor = 0;
var t1 = OnStopWatch(() =>
{
for(var i = 0; i < list1.Count;i++)
{
var item1 = list1[i];
for(var j = 0; j < list2.Count;j++) { var item2 = list2[j]; if (item1 == item2) sumByFor += item1; } } }); var sumByForEach = 0; var t2 = OnStopWatch(() =>
{
foreach(var item1 in list1)
{
foreach(var item2 in list2)
{
if (item1 == item2)
sumByForEach += item1;
}
}
});

var sumByJoinLinq = 0;
var t3 = OnStopWatch(() =>
{
list1.Join(list2, item1 => item1, item2 => item2, (item1, item2) => sumByJoinLinq += item1).Count();
});

this.SetData("Result", new { t1, sumByFor, t2, sumByForEach, t3, sumByJoinLinq, list1 = list1.JoinString(item => item, " "), list2 = list2.JoinString(item => item, " ") });
}

public static IEnumerable Join<TOuter, TInner, TKey, TResult>(this IEnumerable outer, IEnumerable inner, Func<TOuter, TKey> outerKeySelector, Func<TInner, TKey> innerKeySelector, Func<TOuter, TInner, TResult> resultSelector)
{
if (outer == null) throw Error.ArgumentNull("outer");
if (inner == null) throw Error.ArgumentNull("inner");
if (outerKeySelector == null) throw Error.ArgumentNull("outerKeySelector");
if (innerKeySelector == null) throw Error.ArgumentNull("innerKeySelector");
if (resultSelector == null) throw Error.ArgumentNull("resultSelector");
return JoinIterator<TOuter, TInner, TKey, TResult>(outer, inner, outerKeySelector, innerKeySelector, resultSelector, null);
}

static IEnumerable JoinIterator<TOuter, TInner, TKey, TResult>(IEnumerable outer, IEnumerable inner, Func<TOuter, TKey> outerKeySelector, Func<TInner, TKey> innerKeySelector, Func<TOuter, TInner, TResult> resultSelector, IEqualityComparer comparer)
{
Lookup<TKey, TInner> lookup = Lookup<TKey, TInner>.CreateForJoin(inner, innerKeySelector, comparer);
foreach (TOuter item in outer)
{
Lookup<TKey, TInner>.Grouping g = lookup.GetGrouping(outerKeySelector(item), false);
if (g != null)
{
for (int i = 0; i < g.count; i++)
{
yield return resultSelector(item, g.elements[i]);
}
}
}
}

internal static Lookup<TKey, TElement> CreateForJoin(IEnumerable source, Func<TElement, TKey> keySelector, IEqualityComparer comparer)
{
Lookup<TKey, TElement> lookup = new Lookup<TKey, TElement>(comparer);
foreach (TElement item in source)
{
TKey key = keySelector(item);
if (key != null) lookup.GetGrouping(key, true).Add(item);
}
return lookup;
}

internal Grouping GetGrouping(TKey key, bool create)
{
int hashCode = InternalGetHashCode(key);
for (Grouping g = groupings[hashCode % groupings.Length]; g != null; g = g.hashNext)
if (g.hashCode == hashCode && comparer.Equals(g.key, key)) return g;
if (create)
{
if (count == groupings.Length) Resize();
int index = hashCode % groupings.Length;
Grouping g = new Grouping();
g.key = key;
g.hashCode = hashCode;
g.elements = new TElement[1];
g.hashNext = groupings[index];
groupings[index] = g;
if (lastGrouping == null)
{
g.next = g;
}
else
{
g.next = lastGrouping.next;
lastGrouping.next = g;
}
lastGrouping = g;
count++;
return g;
}
return null;
}