Pandas - extracting month and year from index

Question

I have a dataframe with datetime as index. How can I extract year and month from the index? Below is my dataframe.

            1. open   2. high    3. low  4. close   5. volume
date                                                         
2019-01-07   101.64  103.2681  100.9800    102.06  35656136.0
2019-01-08   103.04  103.9700  101.7134    102.80  31294058.0

apparently df["index"].dt.month or df["date"].dt.month doesnt work.

Answer 1

You can take below example, However you can have the details usage from Docs pandas.DatetimeIndex

Example DataFrame:

>>> df
                              name  age favorite_color  grade  birth_date
Willard Morris      Willard Morris   20           blue     88  01-02-1996
Al Jennings            Al Jennings   19            red     92  08-05-1997
Omar Mullins          Omar Mullins   22         yellow     95  04-28-1996
Spencer McDaniel  Spencer McDaniel   21          green     70  12-16-1995

1) To extract year:

>>> df['year'] = pd.DatetimeIndex(df['birth_date']).year
>>> df.head()
                              name  age favorite_color  grade  birth_date  year
Willard Morris      Willard Morris   20           blue     88  01-02-1996  1996
Al Jennings            Al Jennings   19            red     92  08-05-1997  1997
Omar Mullins          Omar Mullins   22         yellow     95  04-28-1996  1996
Spencer McDaniel  Spencer McDaniel   21          green     70  12-16-1995  1995

2) To extract month:

>>> df['month'] = pd.DatetimeIndex(df['birth_date']).month
>>> df.head()
                              name  age favorite_color  grade  birth_date  year  month
Willard Morris      Willard Morris   20           blue     88  01-02-1996  1996      1
Al Jennings            Al Jennings   19            red     92  08-05-1997  1997      8
Omar Mullins          Omar Mullins   22         yellow     95  04-28-1996  1996      4
Spencer McDaniel  Spencer McDaniel   21          green     70  12-16-1995  1995     12

3) To extract year_with_month:

>>> df['month_year'] = pd.to_datetime(df['birth_date']).dt.to_period('M')
>>> df
                              name  age favorite_color  grade  birth_date  year  month month_year
Willard Morris      Willard Morris   20           blue     88  01-02-1996  1996      1    1996-01
Al Jennings            Al Jennings   19            red     92  08-05-1997  1997      8    1997-08
Omar Mullins          Omar Mullins   22         yellow     95  04-28-1996  1996      4    1996-04
Spencer McDaniel  Spencer McDaniel   21          green     70  12-16-1995  1995     12    1995-12

Answer 2

Use DatetimeIndex.year and DatetimeIndex.month, dt is used for select column:

print (df.index)
            1. open   2. high    3. low  4. close   5. volume
date                                                         
2019-01-07   101.64  103.2681  100.9800    102.06  35656136.0
2019-01-08   103.04  103.9700  101.7134    102.80  31294058.0


df.index = pd.to_datetime(df.index)

y = df.index.year
m = df.index.month

print (y)
Int64Index([2019, 2019], dtype='int64', name='date')

print (m)
Int64Index([1, 1], dtype='int64', name='date')