# purrr v0.2.4

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## Functional Programming Tools

A complete and consistent functional programming toolkit for R.

## Readme

# purrr

## 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 R^{2}.

```
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 | |

array-coercion | Coerce array to list | |

as_mapper | Convert an object into a mapper function | |

accumulate | Accumulate recursive folds across a list | |

along | Helper to create vectors with matching length. | |

keep | Keep or discard elements using a predicate function. | |

list_modify | Modify a list | |

lmap | Apply a function to list-elements of a list | |

map | Apply a function to each element of a vector | |

map2 | Map over multiple inputs simultaneously. | |

transpose | Transpose a list. | |

vec_depth | Compute the depth of a vector | |

lift | Lift the domain of a function | |

when | Match/validate a set of conditions for an object and continue with the action associated with the first valid match. | |

cross | Produce all combinations of list elements | |

detect | Find the value or position of the first match. | |

invoke | Invoke functions. | |

is_numeric | Test is an object is integer or double | |

prepend | Prepend a vector | |

purrr-package | purrr: Functional Programming Tools | |

rerun | Re-run expressions multiple times. | |

safely | Capture side effects. | |

every | Do every or some elements of a list satisfy a predicate? | |

flatten | Flatten a list of lists into a simple vector. | |

head_while | Find head/tail that all satisfies a predicate. | |

imap | Apply a function to each element of a vector, and its index | |

null-default | Default value for NULL. | |

partial | Partial apply a function, filling in some arguments. | |

set_names | Set names in a vector | |

splice | Splice objects and lists of objects into a list | |

%>% | Pipe operator | |

pluck | Pluck out a single an element from a vector or environment | |

reduce | Reduce a list to a single value by iteratively applying a binary function. | |

reexports | Objects exported from other packages | |

as_vector | Coerce a list to a vector | |

compose | Compose multiple functions | |

get-attr | Infix attribute accessor | |

has_element | Does a list contain an object? | |

modify | Modify elements selectively | |

negate | Negate a predicate function. | |

rbernoulli | Generate random sample from a Bernoulli distribution | |

rdunif | Generate random sample from a discrete uniform distribution | |

No Results! |

## Vignettes of purrr

Name | ||

other-langs.Rmd | ||

No Results! |

## Last month downloads

## 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 |

LazyData | true |

RoxygenNote | 6.0.1 |

NeedsCompilation | yes |

Packaged | 2017-10-18 13:06:58 UTC; hadley |

Repository | CRAN |

Date/Publication | 2017-10-18 20:19:51 UTC |

suggests | covr , dplyr (>= 0.4.3) , knitr , rmarkdown , testthat |

imports | magrittr (>= 1.5) , rlang (>= 0.1) , tibble |

depends | R (>= 3.1) |

Contributors | RStudio, Hadley Wickham |

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