Extracting column names with condition from a data frame

Question

dput(new)
structure(list(ID = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 
13, 14, 15, 16, 17, 18, 19, 20, 21, 22), A1 = c(1, 1, 1, 1, 0, 
0, 0, 1, 0, 0, 1, 0, 0, 0, 0,         


        

Answer 1

Here is a one liner via base R using stack and aggregate,

aggregate(ind ~ ID, 
          subset(cbind(ID = new$ID, stack(replace(new, new == 0, '')[-1])), values == 1), 
          toString)

which gives,

   ID    ind
1   1 A1, A2
2   2 A1, A2
3   3     A1
4   4     A1
5   6 A2, A8
6   7 A6, A8
7   8 A1, A8
8   9 A6, A8
9  10     A8
10 11 A1, A8
11 12     A6
12 13 A5, A8
13 15     A8
14 16     A8
15 17     A8
16 18     A8
17 19     A8
18 20     A8
19 21     A7