Segregating data based on last 3 months and this time last year - pandas

Question

I need to filter out my data into two different index.
(1) last three months, includes December as current month minus three
(2) current month (December 2019) and current month values from the year before
pDate Name Date Year Month
11/17/2019 12:18 A 2019/11 2019 11
12/23/2018 11:52 B 2018/12 2018 12
12/1/2019 11:42 C 2019/12 2019 12
12/10/2018 14:31 D 2018/12 2018 12
12/14/2018 12:42 E 2018/12 2018 12
10/15/2019 15:19 F 2019/10 2019 10
10/23/2019 10:50 G 2019/10 2019 10
12/2/2018 15:14 H 2018/12 2018 12
I was able to group them based upon their last 3 months values, relatively quick as:
df1 = df.sort_values(by="pDate",ascending=True).set_index("pDate").last("3M")
How do I get a dataframe which maps December 2019 (current month) and December 2018 only.

Answer 1

Idea is create month periods by Series.dt.to_period and then you can subtract values for past periods filtering by Series.between with boolean indexing:
$changed sample datetimes
df['pDate'] = pd.to_datetime(df['pDate'])
df = df.sort_values(by="pDate")
print (df)
pDate Name Date Year Month
7 2018-12-02 15:14:00 H 2018/12 2018 12
4 2018-12-14 12:42:00 E 2018/12 2018 12
3 2019-10-10 14:31:00 D 2018/12 2018 12
5 2019-10-15 15:19:00 F 2019/10 2019 10
6 2019-10-23 10:50:00 G 2019/10 2019 10
2 2019-11-01 11:42:00 C 2019/12 2019 12
1 2019-12-23 11:52:00 B 2018/12 2018 12
0 2020-01-17 12:18:00 A 2019/11 2019 11
nowp = pd.to_datetime('now').to_period('m')
print (nowp)
2020-01
df['per'] = df['pDate'].dt.to_period('m')
df = df[df['per'].between(nowp-4, nowp-1) | df['per'].eq(nowp-13)]
print (df)
pDate Name Date Year Month per
7 2018-12-02 15:14:00 H 2018/12 2018 12 2018-12
4 2018-12-14 12:42:00 E 2018/12 2018 12 2018-12
3 2019-10-10 14:31:00 D 2018/12 2018 12 2019-10
5 2019-10-15 15:19:00 F 2019/10 2019 10 2019-10
6 2019-10-23 10:50:00 G 2019/10 2019 10 2019-10
2 2019-11-01 11:42:00 C 2019/12 2019 12 2019-11
1 2019-12-23 11:52:00 B 2018/12 2018 12 2019-12
Detail:
print (nowp)
2020-01
print (nowp-1)
2019-12
print (nowp-13)
2018-12
print (nowp-4)
2019-09