滚动平均值，在数据框熊猫python中返回nan

Question

所以我一直在尝试计算移动平均线，并且在输出时由于某种原因它给了我NaN

import pandas as pd
import pandas_datareader.data as web
import numpy as np
currentTime = datetime.now().date()

f = web.DataReader('goog', 'yahoo', start=2014-1-1, end=currentTime)
ma_50 = pd.rolling_mean(f, window=50)
print(ma_50)

输出只是给我日期，而我想要的值似乎是NaN如下所示：

2012-01-03         NaN         NaN         NaN         NaN        NaN   

Answer 1

您希望获得50天的滚动平均值，因此前49天将没有数据。尝试使用更少的平均值即可：

import pandas as pd
import pandas_datareader.data as web
import datetime
import numpy as np

currentTime = datetime.datetime.now().date()
df = web.DataReader('goog','yahoo', start='2016-5-1',end='2016-5-15')

ma_3 = pd.rolling_mean(df, window=3)

print(ma_3)

输出：

                  Open        High         Low       Close        Volume  \
Date                                                                       
2016-05-02         NaN         NaN         NaN         NaN           NaN   
2016-05-03         NaN         NaN         NaN         NaN           NaN   
2016-05-04  694.996663  699.410014  690.670003  695.423340  1.621233e+06   
2016-05-05  695.019999  699.970011  692.243327  696.496663  1.632333e+06   
2016-05-06  695.523336  704.643331  694.278992  702.750000  1.730700e+06   
2016-05-09  702.693339  710.963338  701.275655  708.483337  1.670633e+06   
2016-05-10  709.043335  718.023336  707.942322  715.733337  1.632533e+06   
2016-05-11  717.386658  722.230001  712.839986  717.123332  1.586100e+06   
2016-05-12  719.073324  722.409993  712.506653  717.259990  1.536867e+06   
2016-05-13  717.466655  720.130656  710.353333  713.143331  1.451600e+06   

             Adj Close  
Date                    
2016-05-02         NaN  
2016-05-03         NaN  
2016-05-04  695.423340  
2016-05-05  696.496663  
2016-05-06  702.750000  
2016-05-09  708.483337  
2016-05-10  715.733337  
2016-05-11  717.123332  
2016-05-12  717.259990  
2016-05-13  713.143331