4_Merge

1. rbind: row로 붙이기(밑으로)

ex1 <- data.frame(matrix(c(1,2,3,1,1,1,2,2,2), ncol=3))
names(ex1) <- c("pid", "x", "y")
ex1

##   pid x y
## 1   1 1 2
## 2   2 1 2
## 3   3 1 2

ex2 <-data.frame(matrix(c(1,2,3,3,3,3,4,4,4), ncol=3))
names(ex2) <- c("pid", "x", "y")
ex2

##   pid x y
## 1   1 3 4
## 2   2 3 4
## 3   3 3 4

ex3 <- rbind(ex1, ex2)
ex3

##   pid x y
## 1   1 1 2
## 2   2 1 2
## 3   3 1 2
## 4   1 3 4
## 5   2 3 4
## 6   3 3 4

2. cbind: column을 붙이기(옆으로)

ex1 <- data.frame(matrix(c(1,2,3,1,1,1,2,2,2), ncol=3))
names(ex1) <- c("pid", "x", "y")
ex1

##   pid x y
## 1   1 1 2
## 2   2 1 2
## 3   3 1 2

ex2 <-data.frame(matrix(c(1,2,3,3,3,3,4,4,4), ncol=3))
names(ex2) <- c("pid", "w", "z")
ex2

##   pid w z
## 1   1 3 4
## 2   2 3 4
## 3   3 3 4

ex3 <- cbind(ex1, ex2) #pid가 중복됨! 그러면? merge
ex3

##   pid x y pid w z
## 1   1 1 2   1 3 4
## 2   2 1 2   2 3 4
## 3   3 1 2   3 3 4

3. merge

참고: (https://rfriend.tistory.com/51)

ex1 <- data.frame(matrix(c(1,2,3,1,1,1,2,2,2), ncol=3))
names(ex1) <- c("pid", "x", "y")
ex1

##   pid x y
## 1   1 1 2
## 2   2 1 2
## 3   3 1 2

ex2 <-data.frame(matrix(c(1,2,4,3,3,3,4,4,4), ncol=3))
names(ex2) <- c("pid", "w", "z")
ex2

##   pid w z
## 1   1 3 4
## 2   2 3 4
## 3   4 3 4

ex3 <- merge(ex1, ex2, by=c("pid") #공통변수인 pid 중심으로 열로 붙여라
             , all = T) #all = F면 pid = 1, 2인 애들(공통된 애들)만
ex3

##   pid  x  y  w  z
## 1   1  1  2  3  4
## 2   2  1  2  3  4
## 3   3  1  2 NA NA
## 4   4 NA NA  3  4