In base R, an object’s user-defined attributes are lost when common functions such as subset, extend, extract, etc. are used.1 This is due to R’s functional nature. The language is designed to encourage creating function that yield return values that are distinct from the inputs. While this often works well, the language has left attribute management to developers. The problem is, this “default”" behavior is often undesirable. It is tedious to try manage attribute across these operations. It leads to confusion, boilerplate code and source for errors.
sticky package alleviates this shortcomings by providing a simple mechanism for preserving attributes. By marking objects
sticky, attributes become resilient to the common data operations, e.g. subset/extend/append or when inserted into or extracted from recursive (list-like) objects such as data frames or data tables. ‘sticky’ works on both atomic and recursive objects.
This allows R object to behave similar to other object-oriented programming languages while retaining its functional nature. There isn’t much to the package. The
sticky function and it’s complement,
unstick are the only exported functions.
Here is an simple example of a sticky attribute in action. Under base R, attributes do not survive a slice/subset/
x <- 1:5 attr(x, 'foo') <- 'bar' attr(x[1:3],'foo') # NULL -- attribute was lost by the subset
To ensure that the attributes get preserved, simply declare the object as
x <- sticky(x) attr(x[1:3],'foo') # 'bar' -- attribute preserved during subset
sticky() works for vectors inside table-like objects ( i.e. data.frames and data.tables), preserving their attributes during table operations.
df <- data.frame( sticky = sticky( structure(1:5, foo="bar") ), nonstick = structure( letters[1:5], foo="bar" ) ) attr( df[2:3,"nonstick"], 'foo' ) # NULL attr( df[2:3,"sticky"], 'foo' ) # bar
If all elements of a list or a data.frame need to behave in a sticky manner, use
df <- sticky_all(df) attr( df[2:3,"nonstick"], 'foo' ) # Now 'baz'
There are a number of things that can be done with
The issue of attribute resilience has been often asked and debated. Here are a few of the most prevalent discussions.
Non user-defined attributes include class and dimension↩