Question

Suppose I have a data frame like this:

df <- data.frame(id = rep(c(1001:1004), each = 3), value = c(1,1,4,1,2,3,2,2,5,1,5,6))

df
     id value
1  1001     1
2  1001     1
3  1001     4
4  1002     1
5  1002     2
6  1002     3
7  1003     2
8  1003     2
9  1003     5
10 1004     1
11 1004     5
12 1004     6

What is a good way to return me the IDs that have value equals to 1 but 3, i.e., any ID that has its corresponding value equals to 3 will be excluded but must have at least one value equals to 1? In this case, ID 1002 has 1 but also has 3 and shall be excluded. ID 1003 doesn’t have any value equals to 1 and shall be excluded too. So ID 1001 and 1004 will be returned. Thanks!

Answer 1

You can get the ID’s that contain 1 with df$id[df$value == 1], and likewise for 3 df$id[df$value == 3]. To exclude one set from the other, you can use setdiff.

In one command: with(df,setdiff(id[value == 1],id[value == 3]))