Pandas：从其他数据帧复制列时出错

Question

我试图将预测列从df_B追加到df_A

df_A['prediction'] = df_B['prediction']

但是该列没有正确复制，我得到了以下错误：

/Users/edamame/workspace/git/tensorplay/venv/lib/python3.7/site-packages/ipykernel_launcher.py:1: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
  """Entry point for launching an IPython kernel.

是否有一种方法可以正确执行列复制而不在数据帧上循环

Answer 1

如果df_A和df_B的形状相同，则可以使用Pandas的pd.concat（）功能

import pandas as pd 

data_A = [['tom', 10], ['nick', 15], ['juli', 14]] 
df_A = pd.DataFrame(data_A, columns = ['Name', 'Age']) 

data_B = [['LA', "M"], ['NY', 'M'], ['SF', 'F']] 
df_B = pd.DataFrame(data_B, columns = ['City', 'Gender']) 

df_B = pd.concat([df_B, df_A[['Name']]], axis = 1)