C# element-wise difference between two lists of numbers

Question

Assume

List<int> diff(List<int> a, List<int> b)
{ 
    // assume same length lists
    List<int> diff= new List<int>(a.Count);
    for (int i=0; i<diff.Count; ++i)
    {
        diff[i] = a[i] - b[i];
    }
    return diff;
}

I would like to have some kind of one-liner do the same, or something that uses a lambda, rather than re-writing all the boilerplate.

for instance, in python, this would be either

[ai-bi for ai,bi in zip(a,b)]

or even

np.array(a) - np.array(b)

---

Is there a nice way to write this in C#? All my searches find ways to remove or add list elements, but nothing about element-wise actions.

Answer 1

Linq has a Zip method as well:

var diff = a.Zip(b, (ai, bi) => ai - bi);

Note that one potential bug in your code is if b has fewer elements than a then you'd get an exception when you try to access an element outside the range of b . Zip will only return items as long as both collections have items, which is effectively the shorter of the two collection lengths.