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 another solution.

x <- apply(df[-1]!=0, 1, function(x) paste(names(df[-1])[x], collapse=","))
names(x) <- df$ID
cbind(x)               # or cbind(x[x!=""]) if you want to remove empty strings

#    x      
# 1  "A1,A2"
# 2  "A1,A2"
# 3  "A1"   
# 4  "A1"   
# 5  ""     
# 6  "A2,A8"
# 7  "A6,A8"
# 8  "A1,A8"
# 9  "A6,A8"
# 10 "A8"   
# 11 "A1,A8"
# 12 "A6"   
# 13 "A5,A8"
# 14 ""     
# 15 "A8"   
# 16 "A8"   
# 17 "A8"   
# 18 "A8"   
# 19 "A8"   
# 20 "A8"   
# 21 "A7"   
# 22 ""