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

# 結合例２
D <- data.frame(id = c(1, 2, NA, 4, 5), varD = 1:5)
E <- data.frame(id = c(1, 2, 3, 4, NA), varD = letters[1:5])
merge(D, E, by = "id")

##   id varD.x varD.y
## 1  1      1      a
## 2  2      2      b
## 3  4      4      d
## 4 NA      3      e

merge(D, E, by = "id", incomparables = NA)  # NAを結合キーから除外

##   id varD.x varD.y
## 1  1      1      a
## 2  2      2      b
## 3  4      4      d