pandas provides several classes of statistical operations that can be applied to a Series or DataFrame object. These reductive methods, when applied to a Series, result in a single value. When applied to a DataFrame, an axis can be specified and the method will then be either applied to each column or row and results in a Series.

The average value is calculated using .mean(). The following calculates the average of the prices for AAPL and MSFT:

In [119]:
   # calc the mean of the values in each column
   one_mon_hist.mean()

Out[119]:
   MSFT     47.493182
   AAPL    112.411364
   dtype: float64

pandas has taken each column and independently calculated the mean for each and returned the results as values in a Series that is indexed with the column names.

The default is to apply the method on axis=0, applying the function to each column. The following code calculates the mean across axis=1:

In [120]:
   # calc the mean of the values in each row
  ...