Top Answers

1. Count unique values by group
   9 votes
2. Is there a R function equivalent to the subset operator [ ], in order to slice by row index?
   7 votes
3. New column based on values ​from other columns AND respecting pre-established rules
   4 votes
4. Deal with missing data in row-wise manipulation
   4 votes
5. cbind a column containing lists maintaining column of lists
   3 votes