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William Dunlap

2015-Jul-08 17:28 UTC

[R] How to assign value to a variable dynamically constructed

You can use an environment instead of a list using the same [[ syntax.  It
is like 'get0(..., inherit=FALSE)' on the left side of the <- and
like
'assign(...)' on the right side.   E.g.,
   myData <- new.env()
   varName <- "v1"
   myData[[varName]] <- 1:10
   myData[[varName]][4] <- myData[[varName]][4] * 100
   myData[[varName]]
   #  [1]   1   2   3 400   5   6   7   8   9  10
   names(myData)
   # [1] "v1"
(Before R-3.2.0 or so, you had to use objects(myData,all=TRUE) if
myData was an environment and names(myData) if it was a list.  Now
names() works for environments.)

It is better to use a dedicated environment (or list) for each set of
related
variables so that name collisions do not cause problems.


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Wed, Jul 8, 2015 at 10:06 AM, Greg Snow <538280 at gmail.com> wrote:
> This is FAQ 7.21.
>
> The most important part of the answer in FAQ 7.21 is the last section
> where it states that it is often easier to use a list rather than
> messing around with trying to dynamically name global variables.
>
> If you tell us what you are trying to accomplish then we may have
> better advice.  The route you are headed down now usually leads to
> inefficient code and hard to find bugs.
>
> On Tue, Jul 7, 2015 at 2:53 PM, Jun Shen <jun.shen.ut at gmail.com>
wrote:
> > Dear list,
> >
> > Let's say we have a variable (id), whose name is dynamically
constructed.
> > This variable represents a vector or data frame with many elements.
Now I
> > want to specifically assign a value to one of the elements. I
couldn't
> get
> > it right.
> >
> > test <- 'id' # "id" is dynamically constructed
through paste()
> >
> > id <- 1:4
> >
> > # I can get the element by doing
> >
> > get(test)[2]
> >
> > # Now I want to assign a value to the second element of this dynamical
> > variable.
> >
> > get(test)[2] <- 5  # doesn't work.
> >
> > Thanks a lot.
> >
> > Jun Shen
> >
> >         [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > 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.
>
>
>
> --
> Gregory (Greg) L. Snow Ph.D.
> 538280 at gmail.com
>
> ______________________________________________
> 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]]

Bastien Tran

2015-Jul-10 16:44 UTC

head link

[R] How to assign value to a variable dynamically constructed

Dear all,

Provided I understood correctly, shouldn't assign() do the trick? Most
similar threads seem to include this approach (among others, indeed).

Regards,
Bastien


On Wednesday, July 8, 2015 at 7:30:04 PM UTC+2, William Dunlap
wrote:> You can use an environment instead of a list using the same [[ syntax.  It
> is like 'get0(..., inherit=FALSE)' on the left side of the <-
and like
> 'assign(...)' on the right side.   E.g.,
>    myData <- new.env()
>    varName <- "v1"
>    myData[[varName]] <- 1:10
>    myData[[varName]][4] <- myData[[varName]][4] * 100
>    myData[[varName]]
>    #  [1]   1   2   3 400   5   6   7   8   9  10
>    names(myData)
>    # [1] "v1"
> (Before R-3.2.0 or so, you had to use objects(myData,all=TRUE) if
> myData was an environment and names(myData) if it was a list.  Now
> names() works for environments.)
> 
> It is better to use a dedicated environment (or list) for each set of
> related
> variables so that name collisions do not cause problems.
> 
> 
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
> 
> On Wed, Jul 8, 2015 at 10:06 AM, Greg Snow <538280 at gmail.com>
wrote:
> 
> > This is FAQ 7.21.
> >
> > The most important part of the answer in FAQ 7.21 is the last section
> > where it states that it is often easier to use a list rather than
> > messing around with trying to dynamically name global variables.
> >
> > If you tell us what you are trying to accomplish then we may have
> > better advice.  The route you are headed down now usually leads to
> > inefficient code and hard to find bugs.
> >
> > On Tue, Jul 7, 2015 at 2:53 PM, Jun Shen <jun.shen.ut at
gmail.com> wrote:
> > > Dear list,
> > >
> > > Let's say we have a variable (id), whose name is dynamically
constructed.
> > > This variable represents a vector or data frame with many
elements. Now I
> > > want to specifically assign a value to one of the elements. I
couldn't
> > get
> > > it right.
> > >
> > > test <- 'id' # "id" is dynamically
constructed through paste()
> > >
> > > id <- 1:4
> > >
> > > # I can get the element by doing
> > >
> > > get(test)[2]
> > >
> > > # Now I want to assign a value to the second element of this
dynamical
> > > variable.
> > >
> > > get(test)[2] <- 5  # doesn't work.
> > >
> > > Thanks a lot.
> > >
> > > Jun Shen
> > >
> > >         [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
> > > 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.
> >
> >
> >
> > --
> > Gregory (Greg) L. Snow Ph.D.
> > 538280 at gmail.com
> >
> > ______________________________________________
> > 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]]
> 
> ______________________________________________
> 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.

William Dunlap

2015-Jul-10 16:58 UTC

head link

[R] How to assign value to a variable dynamically constructed

Yes, assign() and get() can do this, but I think the [[]] syntax is simpler
and makes it easier to switch between lists and environments for
data organization.

E.g., the translation of
   myData[[varName]][4] <- myData[[varName]][4] * 100
where myData is an environment to the get/assign style
would be something like
   tmp <- get(varName, envir=myData)
   tmp[4] <- tmp[4] * 100
   assign(varName, tmp, envir=myData)

Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Fri, Jul 10, 2015 at 9:44 AM, Bastien Tran <bastien.tran at gmail.com>
wrote:
> Dear all,
>
> Provided I understood correctly, shouldn't assign() do the trick? Most
> similar threads seem to include this approach (among others, indeed).
>
> Regards,
> Bastien
>
>
> On Wednesday, July 8, 2015 at 7:30:04 PM UTC+2, William Dunlap wrote:
> > You can use an environment instead of a list using the same [[ syntax.
> It
> > is like 'get0(..., inherit=FALSE)' on the left side of the
<- and like
> > 'assign(...)' on the right side.   E.g.,
> >    myData <- new.env()
> >    varName <- "v1"
> >    myData[[varName]] <- 1:10
> >    myData[[varName]][4] <- myData[[varName]][4] * 100
> >    myData[[varName]]
> >    #  [1]   1   2   3 400   5   6   7   8   9  10
> >    names(myData)
> >    # [1] "v1"
> > (Before R-3.2.0 or so, you had to use objects(myData,all=TRUE) if
> > myData was an environment and names(myData) if it was a list.  Now
> > names() works for environments.)
> >
> > It is better to use a dedicated environment (or list) for each set of
> > related
> > variables so that name collisions do not cause problems.
> >
> >
> > Bill Dunlap
> > TIBCO Software
> > wdunlap tibco.com
> >
> > On Wed, Jul 8, 2015 at 10:06 AM, Greg Snow <538280 at gmail.com>
wrote:
> >
> > > This is FAQ 7.21.
> > >
> > > The most important part of the answer in FAQ 7.21 is the last
section
> > > where it states that it is often easier to use a list rather than
> > > messing around with trying to dynamically name global variables.
> > >
> > > If you tell us what you are trying to accomplish then we may have
> > > better advice.  The route you are headed down now usually leads
to
> > > inefficient code and hard to find bugs.
> > >
> > > On Tue, Jul 7, 2015 at 2:53 PM, Jun Shen <jun.shen.ut at
gmail.com>
> wrote:
> > > > Dear list,
> > > >
> > > > Let's say we have a variable (id), whose name is
dynamically
> constructed.
> > > > This variable represents a vector or data frame with many
elements.
> Now I
> > > > want to specifically assign a value to one of the elements.
I
> couldn't
> > > get
> > > > it right.
> > > >
> > > > test <- 'id' # "id" is dynamically
constructed through paste()
> > > >
> > > > id <- 1:4
> > > >
> > > > # I can get the element by doing
> > > >
> > > > get(test)[2]
> > > >
> > > > # Now I want to assign a value to the second element of this
> dynamical
> > > > variable.
> > > >
> > > > get(test)[2] <- 5  # doesn't work.
> > > >
> > > > Thanks a lot.
> > > >
> > > > Jun Shen
> > > >
> > > >         [[alternative HTML version deleted]]
> > > >
> > > > ______________________________________________
> > > > 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.
> > >
> > >
> > >
> > > --
> > > Gregory (Greg) L. Snow Ph.D.
> > > 538280 at gmail.com
> > >
> > > ______________________________________________
> > > 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]]
> >
> > ______________________________________________
> > 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]]

Bert Gunter

2015-Jul-10 17:50 UTC

head link

[R] How to assign value to a variable dynamically constructed

I'll let Bill respond in detail if he cares to(he is both more
knowledgable and fluent at this than I), but as a nearly unbreakable
rule, get() and assign() should not be used in R. Basically, they
represent a macro (script)-oriented strategy for handling R's objects,
whereas R is designed to use an object-oriented ("everything is an
object") and functional ("all procedures are functions")
approach.
Using get() and assign() leads to messy, confusing, error-prone,
non-portable code in R, and that's why they should be avoided.

For details, you should consult web tutorials, John Chambers's books,
and other books on R programming.

Cheers,
Bert


Bert Gunter

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
   -- Clifford Stoll


On Fri, Jul 10, 2015 at 9:44 AM, Bastien Tran <bastien.tran at gmail.com>
wrote:> Dear all,
>
> Provided I understood correctly, shouldn't assign() do the trick? Most
similar threads seem to include this approach (among others, indeed).
>
> Regards,
> Bastien
>
>
> On Wednesday, July 8, 2015 at 7:30:04 PM UTC+2, William Dunlap wrote:
>> You can use an environment instead of a list using the same [[ syntax. 
It
>> is like 'get0(..., inherit=FALSE)' on the left side of the
<- and like
>> 'assign(...)' on the right side.   E.g.,
>>    myData <- new.env()
>>    varName <- "v1"
>>    myData[[varName]] <- 1:10
>>    myData[[varName]][4] <- myData[[varName]][4] * 100
>>    myData[[varName]]
>>    #  [1]   1   2   3 400   5   6   7   8   9  10
>>    names(myData)
>>    # [1] "v1"
>> (Before R-3.2.0 or so, you had to use objects(myData,all=TRUE) if
>> myData was an environment and names(myData) if it was a list.  Now
>> names() works for environments.)
>>
>> It is better to use a dedicated environment (or list) for each set of
>> related
>> variables so that name collisions do not cause problems.
>>
>>
>> Bill Dunlap
>> TIBCO Software
>> wdunlap tibco.com
>>
>> On Wed, Jul 8, 2015 at 10:06 AM, Greg Snow <538280 at gmail.com>
wrote:
>>
>> > This is FAQ 7.21.
>> >
>> > The most important part of the answer in FAQ 7.21 is the last
section
>> > where it states that it is often easier to use a list rather than
>> > messing around with trying to dynamically name global variables.
>> >
>> > If you tell us what you are trying to accomplish then we may have
>> > better advice.  The route you are headed down now usually leads to
>> > inefficient code and hard to find bugs.
>> >
>> > On Tue, Jul 7, 2015 at 2:53 PM, Jun Shen <jun.shen.ut at
gmail.com> wrote:
>> > > Dear list,
>> > >
>> > > Let's say we have a variable (id), whose name is
dynamically constructed.
>> > > This variable represents a vector or data frame with many
elements. Now I
>> > > want to specifically assign a value to one of the elements. I
couldn't
>> > get
>> > > it right.
>> > >
>> > > test <- 'id' # "id" is dynamically
constructed through paste()
>> > >
>> > > id <- 1:4
>> > >
>> > > # I can get the element by doing
>> > >
>> > > get(test)[2]
>> > >
>> > > # Now I want to assign a value to the second element of this
dynamical
>> > > variable.
>> > >
>> > > get(test)[2] <- 5  # doesn't work.
>> > >
>> > > Thanks a lot.
>> > >
>> > > Jun Shen
>> > >
>> > >         [[alternative HTML version deleted]]
>> > >
>> > > ______________________________________________
>> > > 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.
>> >
>> >
>> >
>> > --
>> > Gregory (Greg) L. Snow Ph.D.
>> > 538280 at gmail.com
>> >
>> > ______________________________________________
>> > 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]]
>>
>> ______________________________________________
>> 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.
>
> ______________________________________________
> 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.

R help - Jul 2015 - How to assign value to a variable dynamically constructed

[R] How to assign value to a variable dynamically constructed

[R] How to assign value to a variable dynamically constructed

[R] How to assign value to a variable dynamically constructed

[R] How to assign value to a variable dynamically constructed