Checking if all elements in a list are unique
What is the best way (best as in the conventional way) of checking whether all elements in a list are unique?
My current approach using a Counter
is:
>>> x = [1, 1, 1, 2, 3, 4, 5, 6, 2]
>>> counter = Counter(x)
>>> for values in counter.itervalues():
if values > 1:
# do something
Can I do better?
Solution 1:
Not the most efficient, but straight forward and concise:
if len(x) > len(set(x)):
pass # do something
Probably won't make much of a difference for short lists.
Solution 2:
Here is a two-liner that will also do early exit:
>>> def allUnique(x):
... seen = set()
... return not any(i in seen or seen.add(i) for i in x)
...
>>> allUnique("ABCDEF")
True
>>> allUnique("ABACDEF")
False
If the elements of x aren't hashable, then you'll have to resort to using a list for seen
:
>>> def allUnique(x):
... seen = list()
... return not any(i in seen or seen.append(i) for i in x)
...
>>> allUnique([list("ABC"), list("DEF")])
True
>>> allUnique([list("ABC"), list("DEF"), list("ABC")])
False
Solution 3:
An early-exit solution could be
def unique_values(g):
s = set()
for x in g:
if x in s: return False
s.add(x)
return True
however for small cases or if early-exiting is not the common case then I would expect len(x) != len(set(x))
being the fastest method.