purrr v0.2.5

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Functional Programming Tools

A complete and consistent functional programming toolkit for R.

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purrr

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Overview

purrr enhances R's functional programming (FP) toolkit by providing a complete and consistent set of tools for working with functions and vectors. If you've never heard of FP before, the best place to start is the family of map() functions which allow you to replace many for loops with code that is both more succinct and easier to read. The best place to learn about the map() functions is the iteration chapter in R for data science.

Installation

# The easiest way to get purrr is to install the whole tidyverse:
install.packages("tidyverse")

# Alternatively, install just purrr:
install.packages("purrr")

# Or the the development version from GitHub:
# install.packages("devtools")
devtools::install_github("tidyverse/purrr")

Usage

The following example uses purrr to solve a fairly realistic problem: split a data frame into pieces, fit a model to each piece, compute the summary, then extract the R2.

library(purrr)

mtcars %>%
  split(.$cyl) %>% # from base R
  map(~ lm(mpg ~ wt, data = .)) %>%
  map(summary) %>%
  map_dbl("r.squared")
#>         4         6         8 
#> 0.5086326 0.4645102 0.4229655

This example illustrates some of the advantages of purrr functions over the equivalents in base R:

  • The first argument is always the data, so purrr works naturally with the pipe.

  • All purrr functions are type-stable. They always return the advertised output type (map() returns lists; map_dbl() returns double vectors), or they throw an errror.

  • All map() functions either accept function, formulas (used for succinctly generating anonymous functions), a character vector (used to extract components by name), or a numeric vector (used to extract by position).

Functions in purrr

Name Description
keep Keep or discard elements using a predicate function.
map Apply a function to each element of a vector
map2 Map over multiple inputs simultaneously.
array-coercion Coerce array to list
as_mapper Convert an object into a mapper function
null-default Default value for NULL.
every Do every or some elements of a list satisfy a predicate?
partial Partial apply a function, filling in some arguments.
detect Find the value or position of the first match.
cross Produce all combinations of list elements
set_names Set names in a vector
get-attr Infix attribute accessor
splice Splice objects and lists of objects into a list
flatten Flatten a list of lists into a simple vector.
invoke Invoke functions.
has_element Does a list contain an object?
transpose Transpose a list.
when Match/validate a set of conditions for an object and continue with the action associated with the first valid match.
is_numeric Test is an object is integer or double
as_vector Coerce a list to a vector
vec_depth Compute the depth of a vector
accumulate Accumulate recursive folds across a list
%>% Pipe operator
compose Compose multiple functions
along Helper to create vectors with matching length.
head_while Find head/tail that all satisfies a predicate.
lmap Apply a function to list-elements of a list
list_modify Modify a list
imap Apply a function to each element of a vector, and its index
rerun Re-run expressions multiple times.
pluck Pluck out a single an element from a vector or environment
modify Modify elements selectively
safely Capture side effects.
prepend Prepend a vector
rdunif Generate random sample from a discrete uniform distribution
rbernoulli Generate random sample from a Bernoulli distribution
purrr-package purrr: Functional Programming Tools
negate Negate a predicate function.
reduce Reduce a list to a single value by iteratively applying a binary function.
reexports Objects exported from other packages
lift Lift the domain of a function
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Details

License GPL-3 | file LICENSE
URL http://purrr.tidyverse.org, https://github.com/tidyverse/purrr
BugReports https://github.com/tidyverse/purrr/issues
VignetteBuilder knitr
Encoding UTF-8
LazyData true
RoxygenNote 6.0.1
NeedsCompilation yes
Packaged 2018-05-29 14:46:54 UTC; lionel
Repository CRAN
Date/Publication 2018-05-29 16:46:33 UTC

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