我比较了三种不同的方法来比较不同的数据集。下面的测试创建一个字符串集合,包含从
0
到
length - 1
的所有数字,然后创建另一个相同范围的集合,但只包含偶数。然后我从第一个集合中挑选出奇数。
使用 Linq Except
public void TestExcept()
{
WriteLine($"Except {DateTime.Now}");
int length = 20000000;
var dateTime = DateTime.Now;
var array = new string[length];
for (int i = 0; i < length; i++)
{
array[i] = i.ToString();
}
Write("Populate set processing time: ");
WriteLine(DateTime.Now - dateTime);
var newArray = new string[length/2];
int j = 0;
for (int i = 0; i < length; i+=2)
{
newArray[j++] = i.ToString();
}
dateTime = DateTime.Now;
Write("Count of items: ");
WriteLine(array.Except(newArray).Count());
Write("Count processing time: ");
WriteLine(DateTime.Now - dateTime);
}
输出
Except 2021-08-14 11:43:03 AM
Populate set processing time: 00:00:03.7230479
2021-08-14 11:43:09 AM
Count of items: 10000000
Count processing time: 00:00:02.9720879
使用 HashSet.Add
public void TestHashSet()
{
WriteLine($"HashSet {DateTime.Now}");
int length = 20000000;
var dateTime = DateTime.Now;
var hashSet = new HashSet<string>();
for (int i = 0; i < length; i++)
{
hashSet.Add(i.ToString());
}
Write("Populate set processing time: ");
WriteLine(DateTime.Now - dateTime);
var newHashSet = new HashSet<string>();
for (int i = 0; i < length; i+=2)
{
newHashSet.Add(i.ToString());
}
dateTime = DateTime.Now;
Write("Count of items: ");
WriteLine(hashSet.Where(s => newHashSet.Add(s)).Count());
Write("Count processing time: ");
WriteLine(DateTime.Now - dateTime);
}
输出
HashSet 2021-08-14 11:42:43 AM
Populate set processing time: 00:00:05.6000625
Count of items: 10000000
Count processing time: 00:00:01.7703057
特殊的HashSet测试:
public void TestLoadingHashSet()
{
int length = 20000000;
var array = new string[length];
for (int i = 0; i < length; i++)
{
array[i] = i.ToString();
}
var dateTime = DateTime.Now;
var hashSet = new HashSet<string>(array);
Write("Time to load hashset: ");
WriteLine(DateTime.Now - dateTime);
}
> TestLoadingHashSet()
Time to load hashset: 00:00:01.1918160
使用 .Contains
public void TestContains()
{
WriteLine($"Contains {DateTime.Now}");
int length = 20000000;
var dateTime = DateTime.Now;
var array = new string[length];
for (int i = 0; i < length; i++)
{
array[i] = i.ToString();
}
Write("Populate set processing time: ");
WriteLine(DateTime.Now - dateTime);
var newArray = new string[length/2];
int j = 0;
for (int i = 0; i < length; i+=2)
{
newArray[j++] = i.ToString();
}
dateTime = DateTime.Now;
WriteLine(dateTime);
Write("Count of items: ");
WriteLine(array.Where(a => !newArray.Contains(a)).Count());
Write("Count processing time: ");
WriteLine(DateTime.Now - dateTime);
}
输出
Contains 2021-08-14 11:19:44 AM
Populate set processing time: 00:00:03.1046998
2021-08-14 11:19:49 AM
Count of items: Hosting process exited with exit code 1.
(Didnt complete. Killed it after 14 minutes)
结论:
- Linq的
Except
在我的设备上比使用HashSets
(n=20,000,000)慢了大约1秒。
- 使用
Where
和Contains
需要很长时间。
有关HashSets的结论:
- 唯一数据
- 确保为类类型正确地重写
GetHashCode
- 如果您复制数据集,则可能需要多达2倍的内存,具体取决于实现方式
HashSet
针对使用IEnumerable
构造函数克隆其他HashSets进行了优化,但是将其他集合转换为HashSets速度较慢(请参见上面的特殊测试)