PERF: Don't sort labels in groupby.ffill/bfill by rhshadrach · Pull Request #56902 · pandas-dev/pandas (original) (raw)

N = 1000000
df = DataFrame(
    {"group": [1] * N + [2] * N, "value": [np.nan, 1.0] * N}
).set_index("group")
df = df.sample(N)

%timeit df.groupby("group").ffill()
gb = df.groupby("group")
gb.ffill()
%timeit gb.ffill()

# main
21.8 ms ± 676 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)
17.5 ms ± 145 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

# PR
10.3 ms ± 159 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)
5.56 ms ± 74.6 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)