The type of a column where all values are NAs.
In datatable, any column can have NA values in it. There is, however,
a special type for a column where all values are NAs:
type’s special property is that it can be used in
place where any other type could be expected.
A column of this type does not occupy any storage space. Unlike other types, it does not use the validity buffer either: all values are known to be invalid.
It converts into pyarrow’s
pa.null() type, or
float64 dtype in numpy.
When converting into pandas, a Series of
object type is created,
consisting of python
DT = dt.Frame([None, None, None]) DT.type