PERF: Period factorization very slow in 0.19.0

[bmoscon]

df = DataFrame(data={'data': np.random.randint(0, 100, size=5500000),
                         'date': [dt(2016, 1, 1)] * 5500000})
for period, g in df.groupby(pd.DatetimeIndex(df.date).to_period('D')):
    print(g)

Expected Output

outputs dataframe

Output of pd.show_versions()

0.19.0

The output is not the issue, the issue is that in any version before 0.19.0, this was incredibly fast, like ~1 second or less. With 0.19.0, after waiting many minutes I just give up.

[shoyer]

Can you simplify the example here to the simplest possible setup? e.g., by removing the groupby?

[TomAugspurger]

It's not the to_period that's slow, so it's probably the groupby.

In [24]: %time p = pd.DatetimeIndex(df.date).to_period('D')
CPU times: user 339 ms, sys: 6.71 ms, total: 345 ms
Wall time: 350 ms

Also, post the actual code you're running if you could (imports too).

[TomAugspurger]

Here's a smaller example,

import time
import pandas as pd

p = pd.period_range('2010-01-01', freq='D', periods=100000)
t0 = time.time()
pd.factorize(p)
t1 = time.time()
print('{}: {:.2f}s'.format(pd.__version__, t1 - t0))

Some outputs:

• 0.18.1: 0.01s
• 0.19.0rc1: 2.96s

[TomAugspurger]

This is probably due to np.asarray(PeriodIndex) not returning an array of integers.

# 0.18.1
In [5]: np.asarray(p)
Out[5]: array([ 14610,  14611,  14612, ..., 114607, 114608, 114609])

# 0.19
In [4]: np.asarray(p)
Out[4]:
array([Period('2010-01-01', 'D'), Period('2010-01-02', 'D'),
       Period('2010-01-03', 'D'), ..., Period('2283-10-14', 'D'),
       Period('2283-10-15', 'D'), Period('2283-10-16', 'D')], dtype=object)

cc @sinhrks I think.

[chris-b1]

Probably just need a check similar to datetimetz around here to view as an int64

https://github.com/pydata/pandas/blob/v0.19.0/pandas/core/algorithms.py#L294

[shoyer]

@MattRijk See http://pandas.pydata.org/pandas-docs/stable/contributing.html

[shoyer]

@MattRijk Personally, I use SublimeText, usually just on a laptop. But this is off topic for this issue.

[jreback]

yeah this is a pretty easy fix, IIRC this was in @sinhrks PeriodBlock PR, but must have been backed out...something like

if is_period_dtype(values):
    values = values.view('i8')