Using dataframe date column in matplotlib

Question

I have a DataFrame with date as a column formatted as ddmmyy (e.g., 08JUN14). I can’t figure out how to format it for use as the x-axis of a matplotlib plot. From experimenting I understand that I need a string since:

datetime.strptime(“01Jul76”, ,"%d%b%y") 
datetime.datetime(1976, 7, 1, 0, 0)

What I’m not understanding is how to format/use the entire DataFrame column? I tried converting the entire column to a string but that obviously isn’t correct (which I think makes sense after seeing the error message).

s = str(df.date)
d = datetime.strptime(s,"%d%b%y")

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Anaconda\lib\_strptime.py", line 325, in _strptime
    (data_string, format))
ValueError: time data "('01Jul76', '01Sep76', … '15Jan15', '19Mar15')" does not match format '%d%b%y'.

I have searched and seen references to this issue but I don’t seem to be getting anywhere. Any guidance is greatly appreciated.

I think your error is that you're trying to convert a series of strings into datetime objects which will not work the error shows that you tried to convert a long string: '01Jul76', '01Sep76', … '15Jan15', '19Mar15' and so this will not match '%d%b%y' which is expecting a single string to convert — EdChum
– EdChum, Commented Apr 17, 2015 at 14:25

EdChum · Accepted Answer · 2015-04-17 14:50:50Z

It looks like you're trying to convert some strings into datetime objects but you can't pass a pandas Series to datetime.strptime as this raises an error:

In [2]:

df = pd.DataFrame({'date':['01Jul76', '01Sep76', '15Jan15', '19Mar15']})
df
Out[2]:
      date
0  01Jul76
1  01Sep76
2  15Jan15
3  19Mar15
In [4]:

import datetime as dt
dt.datetime.strptime(str(df['date']),"%d%b%y")
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-4-d1c7711603e3> in <module>()
      1 import datetime as dt
----> 2 dt.datetime.strptime(str(df['date']),"%d%b%y")

C:\WinPython-64bit-3.4.3.1\python-3.4.3.amd64\lib\_strptime.py in _strptime_datetime(cls, data_string, format)
    498     """Return a class cls instance based on the input string and the
    499     format string."""
--> 500     tt, fraction = _strptime(data_string, format)
    501     tzname, gmtoff = tt[-2:]
    502     args = tt[:6] + (fraction,)

C:\WinPython-64bit-3.4.3.1\python-3.4.3.amd64\lib\_strptime.py in _strptime(data_string, format)
    335     if not found:
    336         raise ValueError("time data %r does not match format %r" %
--> 337                          (data_string, format))
    338     if len(data_string) != found.end():
    339         raise ValueError("unconverted data remains: %s" %

ValueError: time data '0    01Jul76\n1    01Sep76\n2    15Jan15\n3    19Mar15\nName: date, dtype: object' does not match format '%d%b%y'

The easiest thing is to use to_datetime and pass your format string:

In [7]:

df['date'] = pd.to_datetime(df['date'], format='%d%b%y')
df.info()
<class 'pandas.core.frame.DataFrame'>
Int64Index: 4 entries, 0 to 3
Data columns (total 1 columns):
date    4 non-null datetime64[ns]
dtypes: datetime64[ns](1)
memory usage: 64.0 bytes
In [8]:

df
Out[8]:
        date
0 1976-07-01
1 1976-09-01
2 2015-01-15
3 2015-03-19

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