simplify for iteration to linq query

Question

I currently work on a .NET 4.7.1 application. Given is a for loop to compare 2 lists and to check if any Id has changed. If any Id in list 1 is different to any Id in list 2, I need to return null, otherwise the list 2.

I currently solved this issue with a simple for iteration. Nevertheless, I was wondering if I could solve this easier with a LINQ statement.

var list1 = new List<string>
{
  "A",
  "B",
  "C"
};

var list2 = new List<string>
{
  "A",
  "C",
  "B"
};

private List<string> Compare(){

 if (list1 != null)
 {
    for (int i = 0; i < list1.Count; i++)
    {
        if (list1[i] != list2[i])
        {
            return list2;
        }
    }
    return null;
 }

 return list2;
}

Do you know how to solve this instead of a for loop, but with a LINQ statement?

Thanks!

Answer 1

You can use Zip to group the items together to compare them, and then All to make sure they're the same:

private List<string> Compare()
{

 if (list1 == null) return list2;
 if (list1.Count != list2.Count) return null;

 bool allSame = list1.Zip(list2, (first, second) => (first, second))
                     .All(pair => pair.first == pair.second);


 return allSame ? list2 : null;
}

NOTE: The Zip function is used to place both items into a tuple (first, second).

You can also use SequenceEqual

private List<string> Compare()
{

 if (list1 == null) return list2;

 bool allSame = list1.SequenceEqual(list2);      
 return allSame ? list2 : null;
}

Answer 2

This is one linq alternative to the For loop

   private List<string> Compare()
    {
        if (list1 == null) return list2;
        if (list1.Where((x, i) => x != list2[i]).Any())
        {
            return list2;
        }

        return null;
    }