# 結合例1
A <- data.frame(id = 1:5, varA = 1:5)
B <- data.frame(id = 1:5, varB = c(0, 0, 1, 1, 1))
C <- data.frame(id = c(1, 3), varC = c(10, 20))
merge(A, B, by = "id")
## id varA varB
## 1 1 1 0
## 2 2 2 0
## 3 3 3 1
## 4 4 4 1
## 5 5 5 1
merge(A, C, by = "id")
## id varA varC
## 1 1 1 10
## 2 3 3 20
merge(A, C, by = "id", all = T) # NAで埋めて全て表示
## id varA varC
## 1 1 1 10
## 2 2 2 NA
## 3 3 3 20
## 4 4 4 NA
## 5 5 5 NA