检查是否列表<t>包含任何其他列表</t>

Question

I have a list of parameters like this:

public class parameter
{
    public string name {get; set;}
    public string paramtype {get; set;}
    public string source {get; set;}
}

IEnumerable<Parameter> parameters;

And a array of strings i want to check it against.

string[] myStrings = new string[] { "one", "two"};

I want to iterate over the parameter list and check if the source property is equal to any of the myStrings array. I can do this with nested foreach's but i would like to learn how to do it in a nicer way as i have been playing around with linq and like the extension methods on enumerable like where etc so nested foreachs just feel wrong. Is there a more elegant preferred linq/lambda/delegete way to do this.

Thanks

Answer 1

You could use a nested Any() for this check which is available on any Enumerable :

bool hasMatch = myStrings.Any(x => parameters.Any(y => y.source == x));

Faster performing on larger collections would be to project parameters to source and then use Intersect which internally uses a HashSet<T> so instead of O(n^2) for the first approach (the equivalent of two nested loops) you can do the check in O(n) :

bool hasMatch = parameters.Select(x => x.source)
                          .Intersect(myStrings)
                          .Any(); 

Also as a side comment you should capitalize your class names and property names to conform with the C# style guidelines.

Answer 2

Here is a sample to find if there are match elements in another list

List<int> nums1 = new List<int> { 2, 4, 6, 8, 10 };
List<int> nums2 = new List<int> { 1, 3, 6, 9, 12};

if (nums1.Any(x => nums2.Any(y => y == x)))
{
    Console.WriteLine("There are equal elements");
}
else
{
    Console.WriteLine("No Match Found!");
}

Answer 3

If both the list are too big and when we use lamda expression then it will take a long time to fetch . Better to use linq in this case to fetch parameters list:

var items = (from x in parameters
                join y in myStrings on x.Source equals y
                select x)
            .ToList();

Answer 4

list1.Select(l1 => l1.Id).Intersect(list2.Select(l2 => l2.Id)).ToList();

var list1 = await _service1.GetAll();
var list2 = await _service2.GetAll();

// Create a list of Ids from list1
var list1_Ids = list1.Select(l => l.Id).ToList();

// filter list2 according to list1 Ids
var list2 = list2.Where(l => list1_Ids.Contains(l.Id)).ToList();