— Built-in Function: NA (x)
— Built-in Function: NA (n, m)
— Built-in Function: NA (n, m, k, ...)
— Built-in Function: NA (..., class)

Return a matrix or N-dimensional array whose elements are all equal to the special constant used to designate missing values.

— Mapping Function: isna (x)

Return 1 for elements of x that are NA (missing) values and zero otherwise. For example,

          is_NA ([13, Inf, NA, NaN])
               => [ 0, 0, 1, 0 ]