r - 如何匹配不同数据帧中具有不同频率的两列？

Question

我有两个数据框:

df1 = data.frame(ID = c(1,1,1,1,1,1,1,2,2,2,2,3,3,3,4,4,5,5,5,5), stringsAsFactors = F)

df2 = data.frame(Date = c("2000-01-01","2001-01-1","2002-01-01","2003-01-01","2004-01-01"), stringsAsFactors = F)

现在，我想通过以下方式将 df2 中的日期与 df1 中的 ID 进行匹配:

   ID  Date
1   1  2000-01-01
2   1  2000-01-01
3   1  2000-01-01
4   1  2000-01-01
5   1  2000-01-01
6   1  2000-01-01
7   1  2000-01-01
8   2  2001-01-01
9   2  2001-01-01
10  2  2001-01-01
11  2  2001-01-01
12  3  2002-01-01
13  3  2002-01-01
14  3  2002-01-01
15  4  2003-01-01
16  4  2003-01-01
17  5  2004-01-01
18  5  2004-01-01
19  5  2004-01-01
20  5  2004-01-01

基本上，我假设“ID 1 == 2000-01-01”并希望在 ID 中重复出现 1 的次数。其余逻辑相同。

谁能帮帮我？

谢谢!

Answer 1

使用cbind:

cbind(df1, df2[df1$ID,])
#   ID       Date
#1   1 2000-01-01
#2   1 2000-01-01
#3   1 2000-01-01
#4   1 2000-01-01
#5   1 2000-01-01
#6   1 2000-01-01
#7   1 2000-01-01
#8   2  2001-01-1
#9   2  2001-01-1
#10  2  2001-01-1
#11  2  2001-01-1
#12  3 2002-01-01
#13  3 2002-01-01
#14  3 2002-01-01
#15  4 2003-01-01
#16  4 2003-01-01
#17  5 2004-01-01
#18  5 2004-01-01
#19  5 2004-01-01
#20  5 2004-01-01

或合并:

merge(df1, df2, by.x="ID", by.y=0)
#   ID       Date
#1   1 2000-01-01
#2   1 2000-01-01
#3   1 2000-01-01
#4   1 2000-01-01
#5   1 2000-01-01
#6   1 2000-01-01
#7   1 2000-01-01
#8   2  2001-01-1
#9   2  2001-01-1
#10  2  2001-01-1
#11  2  2001-01-1
#12  3 2002-01-01
#13  3 2002-01-01
#14  3 2002-01-01
#15  4 2003-01-01
#16  4 2003-01-01
#17  5 2004-01-01
#18  5 2004-01-01
#19  5 2004-01-01
#20  5 2004-01-01