R help - May 2023 - extract parts of a list before symbol

Suppose I have the following list:

test <- list(a=3,b=5,c=11)

I'm trying to figure out how to extract the characters to the left of 
the equal sign (i.e., I want to extract a list of the variable names, a, 
b and c.

I've tried the permutations I know of involving sub - things like 
sub("\\=.*", "", test), but no matter what I try, sub keeps
returning
(3, 5, 11). In other words, even though I'm trying to extract the 
'stuff' before the = sign, I seem to be successful only at grabbing the 
stuff after the equal sign.

Pointers to the obvious fix? Thanks...

You probably want `names(test)`.

On Thu, May 25, 2023 at 7:58?PM Evan Cooch <evan.cooch at gmail.com>
wrote:
> Suppose I have the following list:
>
> test <- list(a=3,b=5,c=11)
>
> I'm trying to figure out how to extract the characters to the left of
> the equal sign (i.e., I want to extract a list of the variable names, a,
> b and c.
>
> I've tried the permutations I know of involving sub - things like
> sub("\\=.*", "", test), but no matter what I try, sub
keeps returning
> (3, 5, 11). In other words, even though I'm trying to extract the
> 'stuff' before the = sign, I seem to be successful only at grabbing
the
> stuff after the equal sign.
>
> Pointers to the obvious fix? Thanks...
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

On Thu, 25 May 2023 13:29:52 -0400
Evan Cooch <evan.cooch at gmail.com> wrote:
> Suppose I have the following list:
> 
> test <- list(a=3,b=5,c=11)
> 
> I'm trying to figure out how to extract the characters to the left of 
> the equal sign (i.e., I want to extract a list of the variable names,
> a, b and c.
> 
> I've tried the permutations I know of involving sub - things like 
> sub("\\=.*", "", test), but no matter what I try, sub
keeps returning
> (3, 5, 11). In other words, even though I'm trying to extract the 
> 'stuff' before the = sign, I seem to be successful only at grabbing
> the stuff after the equal sign.
> 
> Pointers to the obvious fix? Thanks...
Perhaps names(test) ???

cheers,

Rolf Turner

-- 
Honorary Research Fellow
Department of Statistics
University of Auckland
Stats. Dep't. (secretaries) phone:
         +64-9-373-7599 ext. 89622
Home phone: +64-9-480-4619

Evan,

List names are less easy than data.frame column names so try this:
> test <- list(a=3,b=5,c=11)
> colnames(test)
NULL
> colnames(as.data.frame(test))
[1] "a" "b" "c"

But note an entry with no name has one made up for it.

> test2 <- list(a=3,b=5, 666, c=11)
> colnames(data.frame(test2))
[1] "a"    "b"    "X666" "c"   

But that may be overkill as simply converting to a vector if ALL parts are
of the same type will work too:
> names(as.vector(test))
[1] "a" "b" "c"

To get one at a time:
> names(as.vector(test))[1]
[1] "a"

You can do it even simple by looking at the attributes of your list:
> attributes(test)
$names
[1] "a" "b" "c"
> attributes(test)$names
[1] "a" "b" "c"
> attributes(test)$names[3]
[1] "c"


-----Original Message-----
From: R-help <r-help-bounces at r-project.org> On Behalf Of Evan Cooch
Sent: Thursday, May 25, 2023 1:30 PM
To: r-help at r-project.org
Subject: [R] extract parts of a list before symbol

Suppose I have the following list:

test <- list(a=3,b=5,c=11)

I'm trying to figure out how to extract the characters to the left of 
the equal sign (i.e., I want to extract a list of the variable names, a, 
b and c.

I've tried the permutations I know of involving sub - things like 
sub("\\=.*", "", test), but no matter what I try, sub keeps
returning
(3, 5, 11). In other words, even though I'm trying to extract the 
'stuff' before the = sign, I seem to be successful only at grabbing the 
stuff after the equal sign.

Pointers to the obvious fix? Thanks...

______________________________________________
R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.