A parser and a writer for 'WEKA' Attribute-Relation File Format < https://waikato.github.io/weka-wiki/arff_stable/> in pure R, with no dependencies. As opposed to other R implementations, this package can read standard (dense) as well as sparse files, i.e. those where each row does only contain nonzero components. Unlike 'RWeka', 'yarr' does not require any 'Java' installation nor is dependent on external software. This implementation is generalized from those in packages 'mldr' and 'mldr.datasets'.