如何从基于另一个数组的列表中排除数据？

Question

Is there any way to exclude data from a list depending on whether the list contains one of the ID in another array?

For example, given:

int[] excludedCities = new int[] { 342, 344, 22, 19, 2 };
List<Cities> cities = new List<Cities>(); 

I want to remove the cities with the id in excludedCities array. Is there an easier way than iterating the list?

Answer 1

HashSet<int> excludedCityHash = new HashSet<int>(excludedCities);
IEnumerable<City> filtered = cities.Where(city => !excludedCityHash.Contains(city.ID));

You can do just:

IEnumerable<City> filtered = cities.Where(city => !excludedCities.Contains(city.ID));

... but for more than a small handful of excluded cities, performance will start to suffer.

Answer 2

If you're happy removing the elements from the cities list then you can do:

cities.RemoveAll(c => excludedCities.Contains(c.Id));

otherwise, you can do:

List<Cities> result = cities.Where(c => !excludedCities.Contains(c.Id))
                            .ToList();