CODEWITHSUNDEEP
c#
william007
william007

Reputation: 18545

Add List of string if it can't be found

I have 

List<List<string>> source

which contains for example

{{"a","b"},{"c","d"}}

I also have a 

List<List<string>> target

which contains for example

{{"a","b"},{"e","f"}}

What is the easiest way I could get the List<string> in source that cannot be found in target, be included in the target?

Here {"c","d"} can be found in source but not target, therefore after assignment the target should be

{{"a","b"},{"e","f"},{"c","d"}}

Upvotes: 1

Views: 94

Answers (2)

C&#233;dric Bignon
C&#233;dric Bignon

Reputation: 13022

Use Linq.Union with custom comparer:

target = target.Union(source, new MyListComparer())  // Use the custom comparer to avoid duplication of the equal sequences.
               .ToList();

With the equality comparer (if you want to have order independant comparison use the second choice in the Equals function):

public class MyListComparer : IEqualityComparer<List<string>>
{
    public bool Equals(List<string> x, List<string> y)
    {
        return x.SequenceEqual(y);  // Use this if { "a", "b" } != { "a", "b" }
        //return x.Count == y.Count && x.Count == x.Intersect(y).Count();  // Use this if { "a", "b" } == { "a", "b" }
    }

    public int GetHashCode(List<string> obj)
    {
        // GetHashCode is used to make the comparison faster by not comparing two elements that does not have the same hash code.
        // GetHashCode must satisfy the following condition
        //  (x == y) implies (GetHashCode(x) == GetHashCode(y))
        // If your are extremely lazy, you can always return 0 but then the complexity of Union will be quadratic instead of linear.
        return obj.Sum(item => item.GetHashCode());
    }
}

Upvotes: 3

Corey Adler
Corey Adler

Reputation: 16149

You could use LINQ:

target = source.Union(target).Distinct(new YourComparer()).ToList();

Then you would need to create a new class that inherits from IEqualityComparer (see here for an example of doing that) that would do the exact comparisons that you want.

Upvotes: 0

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