如何比较pandas Python 2.7中给定DataFrame中的两个单元格

Question

This is the code that I am using.

from datetime import date, datetime, timedelta
import pandas_datareader.data as web
todays_date = date.today()
n = 30
date_n_days_ago = date.today() - timedelta(days=n)
stock_data = web.DataReader('ACC.NS', 'yahoo', date_n_days_ago, todays_date)
stock_data = stock_data[stock_data.Volume != 0].tail(20)
stock_data = stock_data[['Adj Close']]

Now I go to ipython termnal and type:

stock_data['Adj Close'].iloc[[19]] > stock_data['Adj Close'].iloc[[0]]

then the output I get is:

Date

2016-02-18    True

But when I go to my IPython (or my editor Spyder) and code:

if stock_data['Adj Close'].iloc[[19]] > stock_data['Adj Close'].iloc[[0]]:
    print " greater"

the output I get is:

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

MY DOUBT: Why does this happen ?

Presently I have found a workaround code:

adj_close_list = stock_data.values.T.tolist()
if adj_close_list[0][19] > adj_close_list[0][0]:
    print "greater"
else:
    print "less"

Is there any way I can do away with this workaround and directly compare two cells in a DataFrame?

Answer 1

Remove the extra [] :

if stock_data['Adj Close'].iloc[19] > stock_data['Adj Close'].iloc[0]:
    print('greater')
else:
    print('less')

This gives you a float, ie a cell:

>>> stock_data['Adj Close'].iloc[19]
1256.3499999999999

But this gives you a series:

>>> stock_data['Adj Close'].iloc[[19]]
Date
2016-02-18    1.256E+03
Name: Adj Close, dtype: float64

When you compare two series you get another series, which you cannot use in an if statement directly.