Purrr

Purrr is an R package that provides a cohesive toolkit for functional programming, emphasizing predictable, type-stable operations on lists and vectors. It is part of the tidyverse and was created by Hadley Wickham to supplement the base R apply family with a consistent, composable API.

The core concept in purrr is mapping: functions that apply a function to each element of a vector or list. The package offers a family of map functions, including map (returns a list), map_lgl, map_int, map_dbl, map_chr (return atomic vectors of booleans, integers, doubles, strings); map2 and pmap apply functions to two or many arguments; and specialized variants like map_dfr and map_dfc for binding results row-wise or column-wise into data frames. Other operations include reduce, accumulate, flatten, and transpose.

For side effects and filtering, purrr provides walk variants (walk, walk2) that return NULL but execute code; keep and discard select elements by predicate; every and some perform logical checks across a collection; wrappers such as safely, possibly, and quietly handle errors or warnings in a controlled manner.

Additional features include as_mapper to convert functions, formulas, or other objects to mappers; pluck to extract elements by name or position; and negate to invert predicates. Purrr emphasizes a consistent interface and compatibility with tidyverse data structures, often used alongside dplyr, tibble, and other packages.