R：为匹配ID分配值

Question

Let's imagine I have a data set that has 3 different variable ids.

RowID , which is basically this: data$rownumber = 1:nrow(data). Then, ID , which is the company identifier. Finally, ID2 , which tells the user which RowID is the closest

RowID = c(1, 2, 3, 4, 5, 6)
ID = c(123, 456, 789, 712, 409, 587)
Price = c(200, 300, 400, 100, 50, 10)
ID2 = c(2, 1, 1, 1, 3, 3)
df = data.frame(RowID, ID, Price, ID2)
df
RowID  ID   Price ID2
1      123   200   2
2      456   300   1
3      789   400   1
4      712   100   1
5      409    50   3
6      587    10   3

I want to replace the values of ID2 by using the values of ID so that my data looks like this:

RowID  ID   Price ID2 ID3
1      123   200   2  456
2      456   300   1  123
3      789   400   1  123
4      712   100   1  123
5      409    50   3  789
6      587    10   3  789

My data is really big, and of course this is just an example on how it looks.

Thanks!

Answer 1

We can just use 'ID2' as numeric index

df$ID3 <- with(df, ID[ID2])
df
#   RowID  ID Price ID2 ID3
#1     1 123   200   2 456
#2     2 456   300   1 123
#3     3 789   400   1 123
#4     4 712   100   1 123
#5     5 409    50   3 789
#6     6 587    10   3 789