Question

I have a list, A

List<int> A = new List<int>() {1,2,3,4,5};

I also have a bool variable S. I want to copy A into another list using LINQ, with a condition: if S is false then copy the negative value of each element in A (e.g. {-1,-2..}) else it will be the same, like {1,2..}

Answer 1

If I understand your question correctly, that’s indeed possible:

var B = (from item in A
         select S ? item : -item).ToList();

Or, using a lambda expression:

var B = A.Select(item => S ? item : -item).ToList();

You can even do that without using the ternary conditional operator:

var B = A.Select(item => {
    if (S) {
        return item;
    } else {
        return -item;
    }
}).ToList();