Why does array_unique sort the values?
What I would like to know is why array_unique() creates a copy of the array, sorts it then removed the duplicates
The source for both functions is available here.
Thanks in advance!
If you think about it algorithmically, the way to remove duplicates is to go through a list, keep track of items you find, and get rid of things that are already in that "found this" list. One easy way to accomplish this is to sort a list. That way it's obvious where to remove duplicates efficiently. Think about you, let alone a computer; which one of these lists is easier to remove duplicates from?
apple banana cantaloupe apple durian apple banana cantaloupe
apple apple apple banana banana cantaloupe cantaloupe durian
Edit: After looking into it a bit (and finding this article), it looks like while the two both get the job done, they are not functionally equivalent, or at least they aren't always. To paraphrase a couple of these points:
- array_unique() sorts the values, as you noted, so array_flip(array_flip()) wouldn't return the same-ordered array -- but this might be desired.
- If the values are objects, then you can't make them keys (right?), i.e. the flip method wouldn't work out of the box on all arrays, whereas the sort method works fine, regardless of the value types.