It can be. That very much depends on what you're trying to do. Note I didn't pick map for efficiency here, more because it pulls the code together with fewer temporary variables at least using my overall style (and fewer of those do tend to lead to more efficiency).

Selectively modifying elements of an array inplace, esp when you only need to touch few, most likely is best left to a for loop. Touching each or almost each and every element it can be a toss-up. When you are building a new array as you iterate over another, map is very likely the clear winner.

Makeshifts last the longest.