Multi tool use

Finding an item in a complex object

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...

4 Answers
4

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)

SelectMany

tests

domain

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

Lists

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


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

Distinct

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, i.e. their set difference. That can easily be done with the Except method.

domain

sourceElements

Except

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.

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());


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.

//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);

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