Assign value to a specific rows (R)

Question

I have a df of 16k+ items. I want to assign values A, B and C to those items based.

Example: I have the following df with 10 unique items

df <- c(1:10)

Now I have three separate vectors (A, B, C) that contain row numbers of the df with values A, B or C.

A <- c(3, 9)
B <- c(2, 6, 8)
C <- c(1, 4, 5, 7, 10)

Now I want to add a new category column to the df and assign values A, B and C based on the row numbers that are in the three vectors that I have. For example, I would like to assign value C to rows 1, 4, 5, 7 and 10 of the df.

I tried to experiment with for loops and if statements to match the value of the vector with the row number of the df but I didn't succeed. Can anybody help out?

Answer 1

Here is a way to assign the new column.

Create the data frame and a list of vectors:

df <- data.frame(n=1:10)
dat <- list( A=c(3, 9), B=c(2, 6, 8), C=c(1, 4, 5, 7, 10) )

Put the data in the desired rows:

df$new[unlist(dat)] <- sub("[0-9].*$","",names(unlist(dat)))

Result:

df
    n new
1   1   C
2   2   B
3   3   A
4   4   C
5   5   C
6   6   B
7   7   C
8   8   B
9   9   A
10 10   C

Answer 2

You could iterate over the names of a list and assign those names to the positions indexed by the successive sets of numeric values:

dat <- list(A=A,B=B,C=C)
for(i in names(dat)){ df$new[ dat[[i]] ] <- i}