CODEWITHSUNDEEP
rpurrr
a111ex
a111ex

Reputation: 23

Extract names from a list using map() function

I already have a list contains all functions in dplyr by using this code

content <- mget(ls("package:dplyr"), inherits = TRUE)
dplyr_functions <- Filter(is.function, content)

The result I wanna get is just like the result of

names(dplyr_functions)

It will be a chr vector containing all function names in dplyr package. But when I use map() function, my code is like:

dplyr_name <- map_chr(dplyr_functions, names)

There is an error said,

"Result 1 must be a single string, not NULL of length 0"

So I just want to know what the error mean? How can I use map_chr to get a vector containing all names in dplyr_functions?

Upvotes: 1

Views: 1964

Answers (1)

A. Suliman
A. Suliman

Reputation: 13135

map loop through the list element's content "value" e.g. dplyr_functions[[1]] and so on, not through the element as in dplyr_functions[1], try both to see the difference. Hence names(dplyr_functions[[1]]) returns NULL and map_chr fails, while names(dplyr_functions[1]) returns %>% and map_chr could work.

So we can loop through the list index and subset using the 2nd method or use imap which designed to loop through the list names. 

library(purrr)
map_chr(seq_along(dplyr_functions), ~names(dplyr_functions[.x])) 
#or
imap_chr(dplyr_functions, ~.y) %>% unname()

Upvotes: 2

Related Questions