我有以下数据框：

Date DV FA1 FA2 FA3 FA4

22/02/2019 200 Lazard NaN NaN NaN

2/02/2019 50 Deutsche Ondra NaN NaN

22/02/2019 120 China Securities Ballas Daiwa Morgan Stanley

我需要将所有FA列连接成一列，同时还要复制Date和DV列。最终结果如下：

Date DV FA

22/02/2019 200 Lazard

2/02/2019 50 Deutsche

2/02/2019 50 Ondra

22/02/2019 120 China Securities

22/02/2019 120 Ballas

22/02/2019 120 Daiwa

22/02/2019 120 Morgan Stanley

解决办法：使用melt与dropna

yourdf=df.melt(['Date','DV']).dropna()

yourdf

Date DV variable value

0 22/02/2019 200 FA1 Lazard

1 2/02/2019 50 FA1 Deutsche

2 22/02/2019 120 FA1 ChinaSecurities

4 2/02/2019 50 FA2 Ondra

5 22/02/2019 120 FA2 Ballas

8 22/02/2019 120 FA3 Daiwa

11 22/02/2019 120 FA4 MorganStanley