matrix - How to find the distance of two lists?

I have two lists as the following:

ab = {1, -1, -1, -1, 1, 1};
ac = {1, -1, -1,  1, 1, 1};

How I can find the difference (more precisely, the edit distance) between them? In this case the result should be 1, since there is one item difference between ab and ac.

Note: in my case, the list elements only take the values 1 and -1, and both lists are one-dimensional of the same length, but it is always nice to see more general solutions (elements are of Reals, lists are matrices, etc.).

Thank you.