如何从不同长度的表中获取数据

Question

Ok, I am sure there is a simple solution to this. Assuming the following data

A <- 1:10
B <- rep("Part A", 10)
C <- 10:19
df1 <- data.frame(A,B,C)

A <- 1:9
B <- rep("Part B", 9)
D <- 20:28
df2 <- data.frame(A,B,D)

Now I want to create df3 which the user specifies which column names. So df3 should be a 2*19 data frame of only A and B

This does not work

df3 <- rbind(df1[A,B], df2[A,B])

I dont want to use common_cols or [,x] function as my real dataset has over 1000 variables, that are not always in the same order.

Answer 1

Your syntax isn't quite right for subsetting. Try

cols <- c("A", "B")
rbind(df1[,cols], df2[,cols])

The columns you want to keep should be a vector of names (or indices/logicals) after the , .