This functions were written to handle different variants of
“other NA” like representations that are usually used in
various external data sources. unknownToNA can help to change
unknown values to NA for work in R, while NAToUnknown is
meant for the opposite and would usually be used prior to export of data
from R. isUnknown is utility function for testing for unknown
values.
All functions are generic and the following classes were tested to work
with latest version: “integer”, “numeric”,
“character”, “factor”, “Date”, “POSIXct”,
“POSIXlt”, “list”, “data.frame” and
“matrix”. For others default method might work just fine.
unknownToNA and isUnknown can cope with multiple values in
unknown, but those should be given as a “vector”. If not,
coercing to vector is applied. Argument unknown can be feed also
with “list” in “list” and “data.frame” methods.
If named “list” or “vector” is passed to argument
unknown and x is also named, matching of names will occur.
Recycling occurs in all “list” and “data.frame” methods,
when unknown argument is not of the same length as x and
unknown is not named.
Argument unknown in NAToUnknown should hold value that is
not already present in x. If it does, error is produced and one
can bypass that with force=TRUE, but be warned that there is no
way to distinguish values after this action. Use at your own risk!
Anyway, warning is issued about new value in x. Additionally,
caution should be taken when using NAToUnknown on factors as
additional level (value of unknown) is introduced. Then, as
expected, unknownToNA removes defined level in unknown. If
unknown="NA", then "NA" is removed from factor levels in
unknownToNA due to consistency with conversions back and forth.
Unknown representation in unknown should have the same class as
x in NAToUnknown, except in factors, where unknown
value is coerced to character anyway. Silent coercing is also applied,
when “integer” and “numeric” are in question. Otherwise
warning is issued and coercing is tried. If that fails, R introduces
NA and the goal of NAToUnknown is not reached.
NAToUnknown accepts only single value in unknown if
x is atomic, while “list” and “data.frame” methods
accept also “vector” and “list”.
“list/data.frame” methods can work on many components/columns. To
reduce the number of needed specifications in unknown argument,
default unknown value can be specified with component ".default". This
matches component/column ".default" as well as all other undefined
components/columns! Look in examples.