df <- structure(list(a = c("A", "A","B","B","C","C","A", "A","B","B","C","C"),
b = c(1,2,1,4,3,10,2,3,1,7,9,-10),
c = c(5,1,2,3,3,1,2,3,9,7,-5,10),
d = c(3,10,1,9,2,1,2,3,3,5,-5,9)),
.Names = c("nome","b","c","d"),
class = "data.frame",row.names = c(NA, -12L))