R语言数据框合并(merge)的几种方式小结

> df1 = data.frame(CustomerId = c(1:6), Product = c(rep("Toaster", 3), rep("Radio", 3))) 
> df1  
> CustomerId  Product
1     1  Toaster
2     2  Toaster
3     3  Toaster
4     4  Radio
5     5  Radio
6     6  Radio

> df2 = data.frame(CustomerId = c(2, 4, 6), State = c(rep("Alabama", 2), rep("Ohio", 1)))
> df   
> CustomerId  State
1     2  Alabama
2     4  Alabama
3     6  Ohio 

 > merge(x = df1, y = df2, by = "CustomerId", all = TRUE)     
 > CustomerId Product  State
 1     1 Toaster  <NA>
 2     2 Toaster  Alabama
 3     3 Toaster  <NA>
 4     4 Radio   Alabama
 5     5 Radio   <NA>
 6     6 Radio   Ohio

> merge(x = df1, y = df2, by = "CustomerId", all.x = TRUE)
> CustomerId Product  State      
1     1 Toaster  <NA>
2     2 Toaster  Alabama
3     3 Toaster  <NA>
4     4 Radio   Alabama
5     5 Radio   <NA>
6     6 Radio   Ohio

> merge(x = df1, y = df2, by = "CustomerId", all.y = TRUE) 
> CustomerId Product  State
1     2 Toaster  Alabama
2     4 Radio   Alabama
3     6 Radio   Ohio

> merge(x = df1, y = df2, by = NULL)
> CustomerId.x Product CustomerId.y  State
1      1 Toaster      2  Alabama
2      2 Toaster      2  Alabama
3      3 Toaster      2  Alabama
4      4 Radio       2  Alabama
5      5 Radio       2  Alabama
6      6 Radio       2  Alabama
7      1 Toaster      4  Alabama
8      2 Toaster      4  Alabama
9      3 Toaster      4  Alabama
10      4 Radio       4  Alabama
11      5 Radio       4  Alabama
12      6 Radio       4  Alabama
13      1 Toaster      6  Ohio
14      2 Toaster      6  Ohio
15      3 Toaster      6  Ohio
16      4 Radio       6  Ohio
17      5 Radio       6  Ohio
18      6 Radio       6  Ohio