在复杂对象中查找项目

Question

I have a sequence of elements string[]:

new string[] { "A", "B", "C", "D" }

And there is also an object consisting of such several sequences object:

List<Test> obj = new List<Test>()
{
    new Test() {Lists = new List<string>() { "A", "B" } },
    new Test() {Lists = new List<string>() { "A", "C" } },
    new Test() {Lists = new List<string>() { "C" } }
};

I want to find the missing element ( "D" ) in all object collections. That's what I got:

private static List<string> FindeMissingElements()
{
    string nonExistentElement = null;

    List<string> nonExistentElements = new List<string>();

    foreach (var elemArr in arr)
    {
        foreach (var elemObj in obj)
        {
            if (elemObj.Lists.Any(a => a.Contains(elemArr)))
            {
                nonExistentElement = null;
                break;
            }

            nonExistentElement = elemArr;
        }

        if (nonExistentElement != null)
            nonExistentElements.Add(nonExistentElement);
    }

    return nonExistentElements;
}

I would like to simplify the code and use LINQ if possible...

Answer 1

//Flatten the complex object - Get all the elements from the complex object into an IEnumerable collection //Flatten the list --

var listB = (from lm in obj select lm.Lists).SelectMany(it => it.ToList());

//Below list A is input elements //use IEnumerable except extension as below - missingElements IEnumerable will have your elements from complex object --

string[] listA = new string[] { "A", "B", "C", "D", "E" }; var missinElements = listA.Except(listB);

Answer 2

First, I would flatten the sources into a list so I have a collection of actual values. To do this, it's best to use SelectMany ( tests is the original list, and domain is the array of possible elements)

var sourceElements = tests.SelectMany(test => test.Lists);

This will get the Lists properties for each test, and join all the results together, so in your example, you'll have a result of

["A", "B", "A", "C", "C"]

You can use Distinct to only get unique items, so the code is

var sourceElements = tests.SelectMany(test => test.Lists).Distinct();

Now, the only thing left to do is to find the items that are in the domain but not in the sourceElements , ie their set difference. That can easily be done with the Except method.

var missing = domain.Except(sourceElements);

So, to put everything together, your method should be:

private static IEnumerable<string> FindMissingElements(
       IEnumerable<Test> tests, IEnumerable<string> domain)
{
   var sourceElements = tests.SelectMany(test => test.Lists).Distinct();
   var missing = domain.Except(sourceElements)
   return missing;
}

Here is a working example.

Answer 3

I think this can help you:

var list1 = new string[] { "A", "B", "C", "D" }
var nonExistentElements = new List<string>(list1);
obj.ForEach(o => nonExistentElements = nonExistentElements.Except(o.Lists).ToList());

Answer 4

I Try and test your question like this:

private static List<string> FindeMissingElements()
{
  var objectArray = new[] {"A", "B", "C", "D"};
  var obj = new List<Test>()
  {
    new Test() {Lists = new List<string>() { "A", "B" } },
    new Test() {Lists = new List<string>() { "A", "C" } },
    new Test() {Lists = new List<string>() { "C" } }
  };
    var missingValues = objectArray.Where(x => !obj.Any(c => c.Lists.Any(v => v == x))).ToList();
    return missingValues.any() ? missingValue:missingValue = new List<string>();
}

With 1 row you can find missing value.

GoodLuck.