This is rather dumb. The only reason there is an intermediate array in the original copy-based code is because the normalization is badly written. After you obtain max and min, normalization is a single map() function, not two.

As for the overall problem: always choose immutability and then make it faster by first taking advantage of optimization patterns that immutability allows you to use safely. In a case like this, doing the normalization lazily is what springs to mind.

If memory allocation and de-allocation is an issue, use more explicit memory management. Though by experience it is rarely the actual problem. There's basically no chance that it is an issue here, Python interpreters aren't stupid enough to give back memory to the OS immediately after a variable falls out of scope.