R list from variables using variable names [duplicate]

Question

I've looked extensively for a solution for this very simple task and though I have a solution, it seems like there must be a better way. The task is to create a list from a set of variables, using the variable names as names for each element in the list, e.g.:

a <- 2
b <- 'foo'
c <- 1:4

My current solution:

named.list <- function(...) { 
    l <- list(...)
    names(l) <- sapply(substitute(list(...)), deparse)[-1]
    l 
}
named.list(a,b,c)

Produces:

$a
[1] 2

$b
[1] "foo"

$c
[1] 1 2 3 4

+1 For reproducible example. I don't think this is a particularly bad way of doing it myself. But you can avoid the sapply call. — Simon O'Hanlon
– Simon O'Hanlon, Commented Jul 24, 2013 at 10:35

Simon O'Hanlon · Accepted Answer · 2013-07-24 10:36:10Z

21

A couple of ways I can think of include mget (make assumptions about the environment your objects are located in):

mget( c("a","b","c") )
$a
[1] 2

$b
[1] "foo"

$c
[1] 1 2 3 4

Or as an edit to your function, you could use, match.call like this:

named.list <- function(...) { 
    l <- list(...)
    names(l) <- as.character( match.call()[-1] )
   l
}
named.list( a,b,c)
$a
[1] 2

$b
[1] "foo"

$c
[1] 1 2 3 4

Or you can do it in one go using setNames like this:

named.list <- function(...) { 
    l <- setNames( list(...) , as.character( match.call()[-1]) ) 
    l
}

named.list( a,b,c)
$a
[1] 2

$b
[1] "foo"

$c
[1] 1 2 3 4

edited Jul 24, 2013 at 10:36

answered Jul 24, 2013 at 10:19

Simon O'Hanlon

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3 Comments

agstudy Over a year ago

+1! I would as.list(match.call())[-1]. and expand.dots = TRUE is set by default

Simon O'Hanlon Over a year ago

@agstudy thanks and I took heed of your tip about expand.dots!

Wart Over a year ago

This won't allow you to name something in the call, e.g. r named.list(a, b, c = 1:4) will not name c. You could set l <- list(...) then add the names from match.call to elements without names in order to keep names for variables named in the call.

MrFlick · Accepted Answer · 2018-03-13 15:46:56Z

10

If you already using tidyverse packages, then you might be interested in using the tibble::lst function which does this

tibble::lst(a, b, c)
# $a
#  [1] 2
#  
# $b
# [1] "foo"
# 
# $c
# [1] 1 2 3 4

answered Mar 13, 2018 at 15:46

MrFlick

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2 Comments

mihagazvoda Over a year ago

Is there a function that does the opposite, creates variables from named list? I can also post a question if you want.

Courvoisier Over a year ago

@mihagazvoda: list2env does what you want

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