pandas stack（）函数可用于转置，但功能绝不仅仅限于转置。真正的转置是df.T

实际上转置是df.T

http://pandas.pydata.org/pandas-docs/stable/reshaping.html#reshaping-and-pivot-tables 

• Reshaping and Pivot Tables
  • Reshaping by pivoting DataFrame objects
  • Reshaping by stacking and unstacking
    • Multiple Levels
    • Missing Data
    • With a MultiIndex
  • Reshaping by Melt
  • Combining with stats and GroupBy
  • Pivot tables
    • Adding margins
  • Cross tabulations
    • Normalization
    • Adding Margins
  • Tiling
  • Computing indicator / dummy variables
  • Factorizing values