Fast, ordered unique items from sequences

unique.py

# We want to get unique items in a sequence, but to keep the order in which they appear.
# There are quite a few solutions here > http://www.peterbe.com/plog/uniqifiers-benchmark
# Good, up to date summary of methods > https://stackoverflow.com/a/17016257/3381305

# Some test data: text...
tdat = 100 * ['c', 'a', 'c', 'b', 'e', 'd', 'f', 'g', 'h', 'i', 'j', 'j']
tarr = np.array(tdat)
tser = pd.Series(tdat)
# ... and numbers.
narr = np.random.randint(0, 10, size=1200)
ndat = narr.tolist()
nser = pd.Series(narr)

# For reference, a naive loop takes about 80 µs on my machine.

# Order preserving

# 🏆 This is the winner: ~18.5 µs on my data.
def unique_fast(seq):
    return list(dict.fromkeys(seq))
  
# This is the most feature-rich. It is:
# - Fast (~21.5 µs on my data)
# - Lazy
# - Supports non-hashable items (eg list of lists)
# - Supports a key
from itertools import filterfalse
def unique_everseen(iterable, key=None):
    # From https://docs.python.org/3/library/itertools.html#itertools-recipes
    "List unique elements, preserving order. Remember all elements ever seen."
    # unique_everseen('AAAABBBCCDAABBB') --> A B C D
    # unique_everseen('ABBCcAD', str.lower) --> A B C D
    seen = set()
    seen_add = seen.add
    if key is None:
        for element in filterfalse(seen.__contains__, iterable):
            seen_add(element)
            yield element
    else:
        for element in iterable:
            k = key(element)
            if k not in seen:
                seen_add(k)
                yield element
                
# Order destroying
# Just use set(seq), it's about 4 times faster than np.unique().