CODEWITHSUNDEEP
rtidyversepurrr
Andrew Jackson
Andrew Jackson

Reputation: 823

Mixing position and names in purrr map input

The purrr::map function provides some shortcuts for selecting list elements: you can use a position by providing an integer, or a name by providing a string. An example here indicates that you can use a vector to deal with nested list elements. For example, 

library(purrr)
library(repurrrsive) #includes example list data
gh_repos %>% map_chr(., c(1, 3))

navigates within each first position to retrieve and return the third list element.

Yet, when I tried to mix input using a position and name, it returns an error:

gh_repos %>% map_chr(., c(1, "full_name"))
#Error: Result 1 is not a length 1 atomic vector

The syntax can be represented several other ways to return the same results:

gh_repos %>% map_chr(c(1,3)) #Shown above
gh_repos %>% map(1) %>% map_chr("full_name")
gh_repos %>% map_chr(~pluck(.x, 1, "full_name"))

The last option was a discovery I made that approaches mixed inputs. I recognize that the mixed vectorized input is of a different class because it includes characters. Is this the reason it produces an error? What changes can I make to use mixed position and name inputs?

Upvotes: 1

Views: 105

Answers (1)

MrFlick
MrFlick

Reputation: 206177

Yes, the problem is the different data classes. When you use c(), everything gets coerced to the same atomic type . So c(1, "full_name") is turned into c("1", "full_name") which is a character vector. And the first list doesn't have a named element with the name "1". If you want to have mixed classes in R, you generally use lists. And it appears that map supports lists. For example

gh_repos %>% map_chr(list(1, "full_name"))
# [1] "gaborcsardi/after"   "jennybc/2013-11_sfu" "jtleek/advdatasci"   "juliasilge/2016-14" 
# [5] "leeper/ampolcourse"  "masalmon/aqi_pdf"

Upvotes: 2

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