データフレームの結合

# 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