Exclusion filters express logic that defines a set of rows that should be
dropped from the dataset. The rows aren't permanently deleted---you can
recover them at any time by removing the exclusion filter---but they are
omitted from all views and calculations, as if they had been deleted.
Usage
exclusion(x)
exclusion(x) <- value
Arguments
x
a Dataset
value
an object of class CrunchLogicalExpr, or NULL
Value
exclusion returns a CrunchFilter if there is one,
else NULL. The setter returns x with the filter set.
Details
Note that exclusion filters work opposite from how "normal" filters work.
That is, a regular filter expression defines the subset of rows to operate
on: it says "keep these rows." An exclusion filter defines which rows to
omit. Applying a filter expression as a query filter will have the
opposite effect if applied as an exclusion. Indeed, applying it as both
query filter and exclusion at the same time will result in 0 rows.