Using data.frame instead of cbind should be helpful
x <- data.frame(col1=c(10, 20), col2=c("[]", "[]"), col3=c("[[1,2]]","[[1,3]]"))
x
col1 col2 col3
1 10 [] [[1,2]]
2 20 [] [[1,3]]
sapply(x, class) # looking into x to see the class of each element
col1 col2 col3
"numeric" "factor" "factor"
As you can see elements from col1 are numeric as you wish.
data.frame can have variables of different class: numeric, factor and character but matrix doesn't, once you put a character element into a matrix all the other will become into this class no matter what clase they were before.