两个数据框的特定联接

Question

I have two data frames: df1 and df2 :

> df1

     ID  Gender      age      cd       evnt     scr     test_dt
1 C0004    MALE       22       1          1      82    7/3/2014
2 C0004    MALE       22       1          2      76    7/3/2014
3 C0005    MALE       22       1          3    1514    7/3/2014
4 C0005    MALE       23       2          1      81   11/3/2014
5 C0006    MALE       23       2          2      75   11/3/2014
6 C0006    MALE       23       2          3     878   11/3/2014

and,

> df2

     ID    hgt    wt     phys_dt
1 C0004     70   147   6/29/2015
2 C0004     70   157   6/27/2016
3 C0005     67   175   6/27/2016
4 C0005     65   171    7/2/2014
5 C0006     69   160   6/29/2015
6 C0006     64   143    7/2/2014

I want to join df1 and df2 in a way that yields the following data frame, call it df3 :

> df3

     ID   Gender      age      cd       evnt     scr     hgt     wt
1 C0004     MALE       22       1          1      82      70    147
2 C0004     MALE       22       1          2      76      70    157
3 C0005     MALE       22       1          3    1514      67    175
4 C0005     MALE       23       2          1      81      65    171
5 C0006     MALE       23       2          2      75      69    160
6 C0006     MALE       23       2          3     878      64    143

I'm trying to add df2$hgt and df2$wt to the proper ID row. The tricky part is that I want to join hgt and wt to the ID row whose dates ( df1$test_dt and df2$phys_dt ) most closely align. I was thinking I could first sort the two data frames by ID then by their respective dates then try and join? I'm not quite sure how to approach this. Thanks.

Answer 1

If you want to murge just matching the df1$ID and df2$ID, the following should do it:

df3 <- left_join(df1, df2, by = c("ID" = "ID"))  

if the date should be matched as well as the ID, you could try:

df3 <- left_join(df1, df2, by = c("ID" = "ID", "test_dt" = "phys_dt")) 

it is in the library(dplyr)