Keyerror when adding a column to a Dataframe (Pandas)

Question

Pandas DataFrame is not really accepting adding a second column, and I cannot really troubleshoot the issue. I am trying to display Moving Averages. The code works fine just for the first one (MA_9), and gives me error as soon I try to add additional MA (MA_20).

Is it not possible in this case to add more than one column?

The code:

import numpy as np
import pandas as pd
import pandas_datareader as pdr
import matplotlib.pyplot as plt


symbol = 'GOOG.US'
start = '20140314'
end = '20180414'
google = pdr.DataReader(symbol, 'stooq', start, end)
print(google.head())

google_close = pd.DataFrame(google.Close)
print(google_close.last_valid_index)
google_close['MA_9'] = google_close.rolling(9).mean()
google_close['MA_20'] = google_close.rolling(20).mean()
# google_close['MA_60'] = google_close.rolling(60).mean()
# print(google_close)
plt.figure(figsize=(15, 10))
plt.grid(True)

# display MA's
plt.plot(google_close['Close'], label='Google_Cls')
plt.plot(google_close['MA_9'], label='MA 9 day')
plt.plot(google_close['MA_20'], label='MA 20 day')
# plt.plot(google_close['MA_60'], label='MA 60 day')
plt.legend(loc=2)
plt.show()

Would be easier to help if error messages were included, but it looks like there is an answer below. — mgrollins
– mgrollins, Commented Oct 2, 2018 at 23:48

halfer · Accepted Answer · 2018-10-02 23:39:12Z

3

Please update your code as below and then it should work:

google_close['MA_9'] = google_close.Close.rolling(9).mean()
google_close['MA_20'] = google_close.Close.rolling(20).mean()

Initially there was only one column data of Close so your old code google_close['MA_9'] = google_close.rolling(9).mean() worked but after this line of code now it has two column and so it does not know which data you are trying to mean. So updating with the column details of data you wanted to mean, it works google_close['MA_20'] = google_close.Close.rolling(20).mean()

edited Oct 2, 2018 at 23:39

halfer

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answered Oct 1, 2018 at 3:17

nandneo

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1 Comment

Max K Over a year ago

Everything makes sense now, Thank you

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