Chapter 2 purrr basics

2.1 map function

2.1.1 I want to…

Start using {purrr}.

2.1.2 Here’s how to:

The base skeleton of {purrr} iteration functions are:

2.1.3 Ok, but why?

In this skeleton:

  • .x is a list, a data.frame or a vector.
  • .f is the function, formula or atomic vector that will be applied on each element of .f.

Here, what map does is applying the function to each element of a list. The returned object is always a list.

2.1.4 See also

2.2 map_* functions

2.2.1 I want to…

Control the output of my iterations.

2.2.2 Here’s how to:

##  [1] 1.000000 1.414214 1.732051 2.000000 2.236068 2.449490 2.645751
##  [8] 2.828427 3.000000 3.162278

2.2.3 Ok, but why?

You can control the output of your map with these functions: map_lgl map_chr map_int map_dbl map_dfr map_dfc.

2.3 Mappers

2.3.1 I want to…

Create a function on the fly.

2.3.2 Here’s how to:

##  [1]  3  4  5  6  7  8  9 10 11 12

2.3.3 Ok, but why?

One sided formulaes, also called mappers, can be created as the .f argument of map. It is build with ~, then .x refers to the element of the list in .x.

When mapping on two elements, you can use .x and .y. With more than two elements, refer to them with ..1, ..2, ..3, etc.

2.4 map on 2 elements

2.4.1 I want to…

map over two lists.

2.4.2 Here’s how to:

##  [1] "a A" "b B" "c C" "d D" "e E" "f F" "g G" "h H" "i I" "j J" "k K"
## [12] "l L" "m M" "n N" "o O" "p P" "q Q" "r R" "s S" "t T" "u U" "v V"
## [23] "w W" "x X" "y Y" "z Z"

2.4.3 Ok, but why?

map2 and friends (map2 map2_lgl map2_int map2_dbl map2_chr map2_dfr map2_dfc) allows to map over two elements.

2.5 map on more elements

2.5.1 I want to…

map over more than two lists.

2.5.3 Ok, but why?

pmap and friends (pmap_lgl pmap_int pmap_dbl pmap_chr pmap_dfr pmap_dfc) allows to map over more than two elements.

2.6 Iteration for side effect

2.6.1 I want to…

Iterate only for side effect.

2.6.2 Here’s how to:

2.6.3 Ok, but why?

walk is the silent conterpart of map, but invisible: you call it just for side effects. map_*, map2_*, pwalk and friends also exists.