Copied from
http://www.cookbook-r.com/Manipulating_data/Comparing_vectors_or_factors_with_NA/.
This function returns `TRUE`

wherever elements are the same, including `NA`

's,
and `FALSE`

everywhere else.

`compareNA(v1, v2)`

- v1
A vector

- v2
A vector

A logical vector, indicating positions where two vectors are same or differ.