R help - Sep 2010 - using variable from for loop in naming new variables

Simple one here ... but can't get it to work ...

for (i in 1:4){
    paste("stuff",[i]),sep="") <- 3 + i
}

ls()
rm(list=ls())



I just want it to create 4 new variables called stuff1, stuff2, stuff3, stuff4
with the corresponding assignments.  I realise that there are more elegant
functions but this is just a model of a bigger situation.

Thanks

Jim


==============================Dr. Jim Maas
University of East Anglia


	[[alternative HTML version deleted]]

Hi!

assign() should do the job.
But using a list, and filling each element iteratively (with a for loop 
or with *apply() ) might be better, up to you.

Btw, why do you remove your objects?

HTH,
Ivan

Le 9/16/2010 17:44, Maas James Dr (MED) a écrit :
> Simple one here ... but can't get it to work ...
>
> for (i in 1:4){
>      paste("stuff",[i]),sep="")<- 3 + i
> }
>
> ls()
> rm(list=ls())
>
>
>
> I just want it to create 4 new variables called stuff1, stuff2, stuff3,
stuff4 with the corresponding assignments.  I realise that there are more
elegant functions but this is just a model of a bigger situation.
>
> Thanks
>
> Jim
>
>
> ==============================> Dr. Jim Maas
> University of East Anglia
>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@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.
>
-- 
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. Säugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra@uni-hamburg.de

**********
http://www.for771.uni-bonn.de
http://webapp5.rrz.uni-hamburg.de/mammals/eng/mitarbeiter.php


	[[alternative HTML version deleted]]

On Sep 16, 2010, at 11:44 AM, Maas James Dr (MED) wrote:
> Simple one here ... but can't get it to work ...
>
> for (i in 1:4){
>    paste("stuff",[i]),sep="") <- 3 + i
> }
>
> ls()
> rm(list=ls())
 > for (i in 1:4){
+    paste("stuff",[i]),sep="") <- 3 + i
Error: unexpected '[' in:
"for (i in 1:4){
    paste("stuff",["

So the first error pointed you to a problem
 > }
Error: unexpected '}' in "}"

Fixing that error points you to another:
 > for (i in 1:4){
+    paste("stuff", i),sep="") <- 3 + i
Error: unexpected ',' in:
"for (i in 1:4){
    paste("stuff", i),"

And when the syntax gets unsnarled you find that you are trying not  
using the correct semantics for assignment:

 > for (i in 1:4){
+    paste("stuff",i,sep="") <- 3 + i
+ }
Error in paste("stuff", i, sep = "") <- 3 + i :
   target of assignment expands to non-language object

You are currently attempting to "assign" a numeric value to a  
character vector. (That is, once stop throwing an error because  
putting the square brackets around "i" ... and you lose the right- 
paren before the sep argument.)  Try looking at the help page for  
assign (and working more basic examples):

?assign.
>
>
>
> I just want it to create 4 new variables called stuff1, stuff2,  
> stuff3, stuff4 with the corresponding assignments.  I realise that  
> there are more elegant functions but this is just a model of a  
> bigger situation.
>
> Thanks
>
> Jim
>
>
> ==============================> Dr. Jim Maas
> University of East Anglia
>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
David Winsemius, MD
West Hartford, CT

This is FAQ 7.21.

Note that the most important part of the FAQ is the last few lines where it
essentially says "DON'T DO THIS".  If this is just a model for a
bigger situation then definitely Don't Do This, as using assign and global
variables will just create more and bigger future headaches.  Use another data
structure like a list and all this becomes much easier.

-- 
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 Maas James Dr (MED)
> Sent: Thursday, September 16, 2010 9:45 AM
> To: r-help at r-project.org
> Subject: [R] using variable from for loop in naming new variables
> 
> Simple one here ... but can't get it to work ...
> 
> for (i in 1:4){
>     paste("stuff",[i]),sep="") <- 3 + i
> }
> 
> ls()
> rm(list=ls())
> 
> 
> 
> I just want it to create 4 new variables called stuff1, stuff2, stuff3,
> stuff4 with the corresponding assignments.  I realise that there are
> more elegant functions but this is just a model of a bigger situation.
> 
> Thanks
> 
> Jim
> 
> 
> ==============================> Dr. Jim Maas
> University of East Anglia
> 
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> 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.

Dear Jim,

Just to follow up some of the great suggestions with some examples:

#########################################

# Initialize a list, length 4
lstuff <- vector(mode = "list", length = 4)
# store the results of your for loop in it
for (i in 1:4) {
  lstuff[[i]] <- 3 + i
}

# The assign() way
for(i in 1:4) {
  assign(x = paste("stuff", i, sep = ''),
         value = 3 + i, envir = .GlobalEnv)
}

# Now lets see about accessing the data
stuff1
lstuff[[1]]
lstuff # see all elements of the list at once

# So far, so good, but since they are named similarly
# maybe I want to do a similar operation on all of them

# Using the list

lstuff <- lapply(lstuff, '+', y = 3)

# Using the results of the for loop
# stuff1 <- stuff1 + 3
# for every single one, or...

for(i in 1:4) {
  assign(x = paste("stuff", i, sep = ''),
         value = get(paste("stuff", i, sep ='')) + 3,
         envir = .GlobalEnv)
}

# looking again

stuff1
lstuff[[1]]

# if you are concerned because the real thing is  more complex

lstuff[[1]] <- data.frame(A = 1:10, B = 11:20)
lstuff[[2]] <- matrix(rnorm(10))
# you can store much more complex objects in the list
# so no need to worry if "stuff" is actually going to be
# data frames or tables or ...

################################################

Cheers,

Josh

On Thu, Sep 16, 2010 at 8:44 AM, Maas James Dr (MED) <J.Maas at uea.ac.uk>
wrote:
> Simple one here ... but can't get it to work ...
>
> for (i in 1:4){
> ? ?paste("stuff",[i]),sep="") <- 3 + i
> }
>
> ls()
> rm(list=ls())
>
>
>
> I just want it to create 4 new variables called stuff1, stuff2, stuff3,
stuff4 with the corresponding assignments. ?I realise that there are more
elegant functions but this is just a model of a bigger situation.
>
> Thanks
>
> Jim
>
>
> ==============================> Dr. Jim Maas
> University of East Anglia
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

Hi Jim,

First, I think it's better if you reply to the list, other users might 
be interested and have better answers.

Second, as other replies showed you, using a list is actually way easier 
than creating new objects every time. Check especially the reply from 
Joshua Wiley, which gives you great examples and guidance.

Last, regarding rm(list=ls()), what's the point of creating new objects 
in your loop if you remove them right after?! Maybe you intend to do 
stuff on them first. Anyway, I don't use Emacs so not sure why you do it 
that way. Just my limited opinion.

HTH,
Ivan

Le 9/17/2010 12:35, Maas James Dr (MED) a écrit :
>
> Hi Ivan,
>
> Thanks for suggestions, was just hoping to do it all in one step, 
> creating a list and then filling it all seems rather complicated ... 
> will look up *apply.
>
> As for removing objects, I run R interactively from within Emacs (ESS) 
> and stuff hangs around for successive evaluations, not sure where it 
> came from so I clean it out every time ... is there a better way?
>
> Thanks
>
> Jim
>
> Message: 65
>
> Date: Thu, 16 Sep 2010 18:03:29 +0200
>
> From: Ivan Calandra <ivan.calandra@uni-hamburg.de>
>
> To: r-help@r-project.org
>
> Subject: Re: [R] using variable from for loop in naming new variables
>
> Message-ID: <4C923FD1.8000503@uni-hamburg.de>
>
> Content-Type: text/plain
>
>   Hi!
>
> assign() should do the job.
>
> But using a list, and filling each element iteratively (with a for loop
>
> or with *apply() ) might be better, up to you.
>
> Btw, why do you remove your objects?
>
> HTH,
>
> Ivan
>
> Le 9/16/2010 17:44, Maas James Dr (MED) a ?crit :
>
> > Simple one here ... but can't get it to work ...
>
> >
>
> > for (i in 1:4){
>
> >      paste("stuff",[i]),sep="")<- 3 + i
>
> > }
>
> >
>
> > ls()
>
> > rm(list=ls())
>
> >
>
> >
>
> >
>
> > I just want it to create 4 new variables called stuff1, stuff2, 
> stuff3, stuff4 with the corresponding assignments.  I realise that 
> there are more elegant functions but this is just a model of a bigger 
> situation.
>
> >
>
> > Thanks
>
> >
>
> > Jim
>
> >
>
> ==============================>
> Dr. Jim Maas
>
> Research Associate in Network Meta-Analysis
>
> School of Medicine, Health Policy and Practice
>
> CD Annex, Room 1.04
>
> University of East Anglia
>
> Norwich, UK
>
> NR4 7TJ
>
> +44 (0) 1603 591412
>
-- 
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. Säugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra@uni-hamburg.de

**********
http://www.for771.uni-bonn.de
http://webapp5.rrz.uni-hamburg.de/mammals/eng/mitarbeiter.php


	[[alternative HTML version deleted]]