要获得图示结果,可以使用该函数 concat 创建新数据框的列,如下所示:

new_df = pd.DataFrame()

new_df['COL_1'] = pd.concat([df['COL_1'], df['COL_1']])
new_df['COL_8'] = pd.concat([df['COL_2'], df['COL_4']])
new_df['COL_9'] = pd.concat([df['COL_3'], df['COL_5']])
new_df['COL_10'] = pd.concat([pd.DataFrame(np.repeat('COL_2', len(df))), pd.DataFrame(np.repeat('COL_4', len(df)))])

>>> new_df

  COL_1  COL_8   COL_9   COL_10
0     A   col2    col3    COL_2
1     B   col2    col3    COL_2
2     C   col2    col3    COL_2
0     A   col4    col5    COL_4
1     B   col4    col5    COL_4
2     C   col4    col5    COL_4