R语言学习-JOIN的各种实现

library(data.table)
library(dplyr)
A<-data.table(X1=c("a","b","c","d","e"),Y1=c(1,2,3,4,5),Z1=c("num1","num2","num3","num4","num5"))
A
B<-data.table(X2=c("c","d","e","f"),Y2=c(4.4,5.5,6.6,7.7))
B
#LEFT JOIN
left_join(A,B,c("X1" = "X2"))
merge(A,B, by.x = "X1", by.y = "X2",all.x=TRUE)
X1 Y1   Z1  Y2
1  a  1 num1  NA
2  b  2 num2  NA
3  c  3 num3 4.4
4  d  4 num4 5.5
5  e  5 num5 6.6
#RIGHT JOIN
right_join(A,B,c("X1" = "X2"))
merge(A,B, by.x = "X1", by.y = "X2",all.y=TRUE)  X1 Y1   Z1  Y2
1  c  3 num3 4.4
2  d  4 num4 5.5
3  e  5 num5 6.6
4  f NA <NA> 7.7
#INNER JOIN
inner_join(A,B,c("X1" = "X2"))
merge(A,B, by.x = "X1", by.y = "X2")
X1 Y1   Z1  Y2
1  c  3 num3 4.4
2  d  4 num4 5.5
3  e  5 num5 6.6
#FULL JOIN
full_join(A,B,c("X1" = "X2"))
merge(A,B, by.x = "X1", by.y = "X2",all=TRUE)
X1 Y1   Z1  Y2
1:  a  1 num1  NA
2:  b  2 num2  NA
3:  c  3 num3 4.4
4:  d  4 num4 5.5
5:  e  5 num5 6.6
6:  f NA   NA 7.7