R help - Jun 2008 - how to automatically create objects with names from a string list?

Suppose I have a string of objects names:

name <- c("foo", "bar", "baz")

and I would like to use a for loop to automatically create three
objects called "foo", "bar" and "baz" accordingly.
Then how can this
be done" (so that in the workspace, foo = 1, bar = 2 and baz=3)

for (i in name) {
    .....
}

Thanks!

Mark

You can use either assign or eval.

Something like
> name <- c("foo", "bar", "baz")
> for (i in 1:length(name)) assign(name[i],i)


--- On Wed, 4/6/08, Mark Farnell <mark.farnell at gmail.com> wrote:
> From: Mark Farnell <mark.farnell at gmail.com>
> Subject: [R] how to automatically create objects with names from a string
list?
> To: R-help at r-project.org
> Received: Wednesday, 4 June, 2008, 3:15 PM
> Suppose I have a string of objects names:
> 
> name <- c("foo", "bar",
> "baz")
> 
> and I would like to use a for loop to automatically create
> three
> objects called "foo", "bar" and
> "baz" accordingly.  Then how can this
> be done" (so that in the workspace, foo = 1, bar = 2
> and baz=3)
> 
> for (i in name) {
>     .....
> }
> 
> Thanks!
> 
> Mark
> 
> ______________________________________________
> R-help at r-project.org mailing list
> 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.

Or with mapply

name <- c("foo", "bar", "baz")
val <- 1:3
mapply(assign, name, val, pos=1)

Cheers,

Simon.


On Tue, 2008-06-03 at 22:24 -0700, Moshe Olshansky
wrote:
> You can use either assign or eval.
> 
> Something like
> 
> > name <- c("foo", "bar", "baz")
> > for (i in 1:length(name)) assign(name[i],i)
> 
> 
> 
> --- On Wed, 4/6/08, Mark Farnell <mark.farnell at gmail.com> wrote:
> 
> > From: Mark Farnell <mark.farnell at gmail.com>
> > Subject: [R] how to automatically create objects with names from a
string list?
> > To: R-help at r-project.org
> > Received: Wednesday, 4 June, 2008, 3:15 PM
> > Suppose I have a string of objects names:
> > 
> > name <- c("foo", "bar",
> > "baz")
> > 
> > and I would like to use a for loop to automatically create
> > three
> > objects called "foo", "bar" and
> > "baz" accordingly.  Then how can this
> > be done" (so that in the workspace, foo = 1, bar = 2
> > and baz=3)
> > 
> > for (i in name) {
> >     .....
> > }
> > 
> > Thanks!
> > 
> > Mark
> > 
> > ______________________________________________
> > R-help at r-project.org mailing list
> > 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.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
-- 
Simon Blomberg, BSc (Hons), PhD, MAppStat. 
Lecturer and Consultant Statistician 
Faculty of Biological and Chemical Sciences 
The University of Queensland 
St. Lucia Queensland 4072 
Australia
Room 320 Goddard Building (8)
T: +61 7 3365 2506
http://www.uq.edu.au/~uqsblomb
email: S.Blomberg1_at_uq.edu.au

Policies:
1.  I will NOT analyse your data for you.
2.  Your deadline is your problem.

The combination of some data and an aching desire for 
an answer does not ensure that a reasonable answer can 
be extracted from a given body of data. - John Tukey.

Mark,

Others have given answers to the question that you asked, in the spirit of
fortune(108) I am going to answer some of the questions that you should have
asked:

Q1: Should I ever do this?
Short answer: No
Less short answer: probably not
Longer answer: You should only do this once you fully understand why you should
never do this.

Q2: Why should I not do this?
A: There are many reasons, the most important is probably that there are better
ways to accomplish what you want to do. Another important reason is doing this
tends to lead to bugs that are very difficult to find and debug, these types of
constucts lead to accidentally overwriting variables, using a different variable
than you intend, using loops where other tools are better, etc.

Q3: What is a better method to accomplish this?
A: This depends on what all you want to do with these new variables, but for
most cases using a list (or sometimes creating a new environment) will
accomplish what you want much better.  For example:
> tmp <- c('foo','bar','baz')
> mylist <- as.list(1:3)
> names(mylist) <- tmp
> mylist
$foo
[1] 1

$bar
[1] 2

$baz
[1] 3
>
> # or
>
> mylist <- list()
> for(i in seq(along=tmp)){
+ mylist[[ tmp[i] ]] <- i
+ }
> mylist
$foo
[1] 1

$bar
[1] 2

$baz
[1] 3
>
> # access a specific value
> mylist$bar
[1] 2
>
> # do something to all of them
> sapply( mylist, function(x) x+5 )
foo bar baz
  6   7   8
>
> # use more directly
> with( mylist, plot(1:10, 1:10, col=bar, pch=baz) )
>
> # compute new variables based on them
> mylist <- within(mylist, foobar <- foo + bar + baz)
> mylist
$foo
[1] 1

$bar
[1] 2

$baz
[1] 3

$foobar
[1] 6
>
> # save everything
> save(mylist, file='myfile')
>
> # remove everything in one shot
> rm(mylist)
>
Hope this helps,

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
(801) 408-8111


> -----Original Message-----
> From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-project.org] On Behalf Of Mark Farnell
> Sent: Tuesday, June 03, 2008 11:16 PM
> To: R-help at r-project.org
> Subject: [R] how to automatically create objects with names
> from a string list?
>
> Suppose I have a string of objects names:
>
> name <- c("foo", "bar", "baz")
>
> and I would like to use a for loop to automatically create
> three objects called "foo", "bar" and "baz"
accordingly.
> Then how can this be done" (so that in the workspace, foo > 1, bar
= 2 and baz=3)
>
> for (i in name) {
>     .....
> }
>
> Thanks!
>
> Mark
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
>