R help - Feb 2011 - assign value to multiple objects with a given ls pattern

Dear R colleagues,

This seems pretty straight forward but I have been banging my head on this for
some time and can't seem to find a solution

suppose I have something like

a1<-1; a2<-2; a3<-3; a4<-4; b1<-3; b2<-4
I would like to quickly assign to objects with a certain pattern, e.g., those in

ls(pattern="a")

a specific value, e.g., "99", without having to assign each object at
a time.

is there a way I can do this within a "for" cycle? I have tested
several eval and parse statements but with no success.

Regards,

Nuno Prista

____________________________
PhD student
Instituto de Oceanografia
Faculdade de Ci?ncias da Universidade de Lisboa
Campo Grande, Lisboa,
1749-016 Lisboa,
Portugal

Hi Nuno,
Yes, you can do

for(i in ls(pattern="a"))
{
  assign(i, 99)
}

but honestly this is a bad idea. It will try to assign the value of 99
to any object in your workspace that contains an a, which sounds
really scary to me.

Better I think to use a list:

ab.list <- list(a1=1, a2=2, a3=3, a4=4, b1=3, b2=4)
ab.list[grep("a", names(ab.list))] <- 99

Or even just a named vector

ab.vector <- c(a1=1, a2=2, a3=3, a4=4, b1=3, b2=4)
ab.vector[grep("a", names(ab.vector))] <- 99

Best,
Ista

On Mon, Feb 21, 2011 at 4:22 PM, Nuno Prista <nmprista at fc.ul.pt>
wrote:
> Dear R colleagues,
>
> This seems pretty straight forward but I have been banging my head on this
for some time and can't seem to find a solution
>
> suppose I have something like
>
> a1<-1; a2<-2; a3<-3; a4<-4; b1<-3; b2<-4
> I would like to quickly assign to objects with a certain pattern, e.g.,
those in
>
> ls(pattern="a")
>
> a specific value, e.g., "99", without having to assign each
object at a time.
>
> is there a way I can do this within a "for" cycle? I have tested
several eval and parse statements but with no success.
>
> Regards,
>
> Nuno Prista
>
> ____________________________
> PhD student
> Instituto de Oceanografia
> Faculdade de Ci?ncias da Universidade de Lisboa
> Campo Grande, Lisboa,
> 1749-016 Lisboa,
> Portugal
>
> ______________________________________________
> 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.
>


-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org

Hi,

This works for me:
pat <- ls(pattern="^a") ## I would anchor "a" to the
beginning with "^"
for safety!
for (i in seq_along(pat))assign(pat[i], value=99)

Or this with lapply:
lapply(pat, FUN=function(x) assign(x, value=99, envir=.GlobalEnv))

See ?assign

HTH,
Ivan

Le 2/21/2011 17:22, Nuno Prista a ?crit :
> Dear R colleagues,
>
> This seems pretty straight forward but I have been banging my head on this
for some time and can't seem to find a solution
>
> suppose I have something like
>
> a1<-1; a2<-2; a3<-3; a4<-4; b1<-3; b2<-4
> I would like to quickly assign to objects with a certain pattern, e.g.,
those in
>
> ls(pattern="a")
>
> a specific value, e.g., "99", without having to assign each
object at a time.
>
> is there a way I can do this within a "for" cycle? I have tested
several eval and parse statements but with no success.
>
> Regards,
>
> Nuno Prista
>
> ____________________________
> PhD student
> Instituto de Oceanografia
> Faculdade de Ci?ncias da Universidade de Lisboa
> Campo Grande, Lisboa,
> 1749-016 Lisboa,
> Portugal
>
> ______________________________________________
> 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.
>
-- 
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. S?ugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra at uni-hamburg.de

**********
http://www.for771.uni-bonn.de
http://webapp5.rrz.uni-hamburg.de/mammals/eng/1525_8_1.php

If instead of having a1, a2, etc. as global variables you put them into a list
then this becomes simple.

The general rule is that if you ever want to do the same (or similar) think to a
set of variable, then they should not have been separate variables, but part of
a bigger one.  Lists work well for this (there are other possibilities as well,
but lists cover most of the cases).

-- 
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 Nuno Prista
> Sent: Monday, February 21, 2011 9:22 AM
> To: r-help at R-project.org
> Subject: [R] assign value to multiple objects with a given ls pattern
> 
> Dear R colleagues,
> 
> This seems pretty straight forward but I have been banging my head on
> this for some time and can't seem to find a solution
> 
> suppose I have something like
> 
> a1<-1; a2<-2; a3<-3; a4<-4; b1<-3; b2<-4
> I would like to quickly assign to objects with a certain pattern, e.g.,
> those in
> 
> ls(pattern="a")
> 
> a specific value, e.g., "99", without having to assign each
object at a
> time.
> 
> is there a way I can do this within a "for" cycle? I have tested
> several eval and parse statements but with no success.
> 
> Regards,
> 
> Nuno Prista
> 
> ____________________________
> PhD student
> Instituto de Oceanografia
> Faculdade de Ci?ncias da Universidade de Lisboa
> Campo Grande, Lisboa,
> 1749-016 Lisboa,
> Portugal
> 
> ______________________________________________
> 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.