Data manipulation in R merge columns

Question

I have a column in a data set A: 1, 1 , 2 , 2, 3, 4, 4, 4, 4, 5, 5. and a data set B B:1, 2, 3, 4, 5

Is there a way how to respectively assign the values of B to the values of A.

The desirable result has to be :

A   B   C
1   v   v
1   b   v
2   n   b
2   m   b
3   k   n
4       m
4       m
4       m
4       m
5       k
5       k

Answer 1

You could try

C <- B[A]
#> C
# [1] "v" "v" "b" "b" "n" "m" "m" "m" "m" "k" "k"

If you want to store this result in a data frame, you could use

length(B) <- length(A) # adapt the length of column B to that of column A
df <- cbind(A, B, C) # generate a matrix with three columns
df[is.na(df)] <- "" # remove the NA entries in column B (replace them with     
                    # an empty string) in the rows where it is not defined
df <- as.data.frame(df) # convert the matrix into a data frame
#> df
#   A B C
#1  1 v v
#2  1 b v
#3  2 n b
#4  2 m b
#5  3 k n
#6  4   m
#7  4   m
#8  4   m
#9  4   m
#10 5   k
#11 5   k

data

A <- c(1, 1, 2, 2, 3, 4, 4, 4, 4, 5, 5)
B <- c("v", "b", "n", "m", "k")

However, if you already have the columns A and B stored in a data frame and you only need to generate column C, you could obtain this result using df$C <- with(df, B[A])