Filters in R

R Outputs

An R Output can refer to a variable called QFilter. Key properties of QFilter are:

• It automatically updates when the filters change.
• If no filters are applied, it takes a value of TRUE.
• If a filter is applied, it has the same length as the number of non-deleted cases in the Data Set.
• Where multiple filters are applied, a single variable is created (using an and operation).
• The Variable Label is available as an attribute (i.e., attr(QFilter, "label")). Where there are multiple filters, they are concatenate as a list (e.g., "Male, 18 to 24 and Tall").
• The Variable Name is available as an attribute (i.e., attr(QFilter, "label")). Where there are multiple names, they are concatenates as with labels.

Approaches to using filters when writing R code

R code typically needs to do the following things when taking filters into account:

• Filter the data. The data may either by passed in to a function in some format, or, extracted indirectly from the environment.
• Clean the data in the filter.
• The name or label of the filter in the output.

The most straightforward way to deal with these is to use an existing analysis as a template (e.g., flipMultivariates::LDA). Base R has a standard function for filtering data called subset.