TypeError: strptime() argument 1 must be string, not float

Question

Good morning!

I have a series of events with associated dates. The event dates are stored as a series of string values in a column within a dataframe that I have loaded into Python. The dataframe contains other columns with values. I would like to convert the values in column "event" into datetime objects, store them in a list, and then plot that list with matplotlib to create a timeseries.

My dataframe looks like this:

         date         value_1    event        other_event
37       07/02/2015   265.09     07/02/2015   NaN
38       08/02/2015   278.59     08/02/2015   NaN
156      06/06/2015   146.07     06/06/2015   NaN
180      30/06/2015   133.56     30/06/2015   NaN
243      01/09/2015   280.27     01/09/2015   01/09/2015

Python tells me that the column data is Name: event, dtype: object, which I assume means it contains string values. I also have the line df.event.apply(str) in my code, which I think will convert the values in my event column into string values.

Then I have this code:

FMT = '%d/%m/%Y'
event_list = []

for i in range(0, len(event)):
    event_list.append(datetime.datetime.strptime(event[i], FMT)) 

However, this line returns an error:

Traceback (most recent call last):

  File "<ipython-input-39-e778a465e858>", line 2, in <module>
    event_list.append(datetime.datetime.strptime(event[i], FMT))

TypeError: strptime() argument 1 must be string, not float

Any advice as to where I'm going wrong will be gratefully received.

Solution

To plot the dataframe in question using matplotlib, you may convert the column in question to datetime using pandas.to_datetime first.

u = u"""i         date         value_1    event        other_event
37       07/02/2015   265.09     07/02/2015   NaN
38       08/02/2015   278.59     08/02/2015   NaN
156      06/06/2015   146.07     06/06/2015   NaN
180      30/06/2015   133.56     30/06/2015   NaN
243      01/09/2015   280.27     01/09/2015   01/09/2015"""

import io
import pandas as pd
import matplotlib.pyplot as plt

df = pd.read_csv(io.StringIO(u), delim_whitespace=True)
df["event"] = pd.to_datetime(df["event"], format="%d/%m/%Y")

plt.plot(df["event"], df["value_1"])
plt.gcf().autofmt_xdate()
plt.show()