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

Something like this?

apply(new[,-1],1,function(x){
  paste0(colnames(new)[which(x==1)+1],collapse=",")
})

 [1] "A1,A2" "A1,A2" "A1"    "A1"    ""      "A2,A8" "A6,A8" "A1,A8" "A6,A8" "A8"    "A1,A8" "A6"   
[13] "A5,A8" ""      "A8"    "A8"    "A8"    "A8"    "A8"    "A8"    "A7"    ""