In python: I've always thought it's funny that of the list functions (map, filter, reduce?), reduce is the one that was removed, but is the only one that I occasionally reach for. (When I remember it doesn't exist, I'm usually happy to write the more readable three-line for loop.)

The other two can be simply expressed as a list comprehension, but afaik you can't with reduce (and if you can, it's probably awful).