小编Pha*_*inh的帖子

样本数据

df <- data.frame(id=c("A","A","A","A","B","B","B","B"),year=c(2014,2014,2015,2015),month=c(1,2),marketcap=c(4,6,2,6,23,2,5,34),return=c(NA,0.23,0.2,0.1,0.4,0.9,NA,0.6))

df1
   id year month marketcap return
1:  A 2014     1         4     NA
2:  A 2014     2         6   0.23
3:  A 2015     1         2   0.20
4:  A 2015     2         6   0.10
5:  B 2014     1        23   0.40
6:  B 2014     2         2   0.90
7:  B 2015     1         5     NA
8:  B 2015     2        34   0.60

所需数据

desired_df <- data.frame(id=c("A","A","A","A","B","B","B","B"),year=c(2014,2014,2015,2015),month=c(1,2),marketcap=c(4,6,2,6,23,2,5,34),return=c(0.23,0.23,0.2,0.1,0.4,0.9,0.75,0.6))

desired_df
  id year month marketcap return
1  A 2014     1         4   0.23
2  A 2014     2         6   0.23 …