Constructing a named list without having to type each object's name twice [duplicate]

Question

In interactive use, I occasionally need to bundle a largish set of objects together in a list. To get a list in which the elements keep their original names, I am forced to write something like list(Object1=Object1, Object2=Object2, ..... , Object25=Object25).

Is there some straightforward way to place a set of named objects in a list, such that they 'keep' their names, without having to type nameXXX=nameXXX for each one?

cars <- mtcars[1:2,1:2]
vowels <- c("a","e","i","o","u")
consonants <- setdiff(letters, vowels)

## I'd like to get this result...
list(consonants=consonants, vowels=vowels, cars=cars)
## $consonants
##  [1] "b" "c" "d" "f" "g" "h" "j" "k" "l" "m" "n" "p" "q" "r" "s" "t" "v" "w" "x"
## [20] "y" "z"
##
## $vowels
## [1] "a" "e" "i" "o" "u"
##
## $cars
##               mpg cyl
## Mazda RX4      21   6
## Mazda RX4 Wag  21   6

## ... but by doing something more like
f(consonants, vowels, cars)

Thanks, @BenBolker -- I'd accept your answer if I could.

Josh O'Brien
– Josh O'Brien

2015-06-10 20:50:52 +00:00
Commented Jun 10, 2015 at 20:50 — Josh O'Brien
– Josh O'Brien, Commented Jun 10, 2015 at 20:50

MrFlick · Accepted Answer · 2015-06-10 19:34:31Z

19

You can get the same structure with

mget(c("vowels", "consonants", "cars"))

but you do have to do have to quote the variable names which isn't super sexy.

answered Jun 10, 2015 at 19:34

MrFlick

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2 Comments

G. Grothendieck Over a year ago

This modification allows unquoted names: mget(sapply(expression(vowels, consonants, cars), paste))

MrFlick Over a year ago

Interesting. I'm kind of surprised paste works like that. I would have expected a deparse.

Josh O'Brien · Accepted Answer · 2015-06-10 19:30:06Z

11

Here's what I used most recently.

It would be nice, though, if there were something more succinct (or something built into base R or a decent package), so please feel free to add other/better answers.

LIST <- function(...) {
    nms <- sapply(as.list(substitute(list(...))), deparse)[-1]
    setNames(list(...), nms)
}

LIST(vowels, consonants, cars)
# $vowels
# [1] "a" "e" "i" "o" "u"
# 
# $consonants
#  [1] "b" "c" "d" "f" "g" "h" "j" "k" "l" "m" "n" "p" "q" "r" "s" "t" "v" "w" "x"
# [20] "y" "z"
# 
# $cars
#               mpg cyl
# Mazda RX4      21   6
# Mazda RX4 Wag  21   6

answered Jun 10, 2015 at 19:30

Josh O'Brien

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Comments

Jthorpe · Accepted Answer · 2015-06-10 19:46:04Z

2

How about:

namedList  <-  function(...){
    out  <-  list(...)
    for(i in seq(length(out)))
        names(out)[i]  <-  as.character(sys.call()[[i+1]])
    out
}

foo = 1
bar = 'Hello world'
namedList(foo,bar)

#> $foo
#> [1] 1
#> 
#> $bar
#> [1] "Hello world"

answered Jun 10, 2015 at 19:46

Jthorpe

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