R help - May 2002 - Converting Character Strings into Object Names

Is there a function to convert character strings to object references.  For
example, I want to name sets of objects based on scenarios and the types of
data being stored.  So the scenarios might be something like c("a",
"b",
"c"), the types of data might have names like c("pass.trp",
"trk.trp",
"cmute.trp"), and I want to assign data to the objects a.pass.trp,
b.pass.trp, c.pass.trp, a.trk.trp, etc.  I'd like to be able to paste the
names together and then use them as an object references.

Brian Gregor, P.E.
Transportation Planning Analysis Unit
Oregon Department of Transportation
Brian.J.GREGOR at odot.state.or.us
(503) 986-4120

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On Fri, 24 May 2002 Brian.J.GREGOR at odot.state.or.us wrote:
> Is there a function to convert character strings to object references.  For
> example, I want to name sets of objects based on scenarios and the types of
> data being stored.  So the scenarios might be something like
c("a", "b",
> "c"), the types of data might have names like
c("pass.trp", "trk.trp",
> "cmute.trp"), and I want to assign data to the objects
a.pass.trp,
> b.pass.trp, c.pass.trp, a.trk.trp, etc.  I'd like to be able to paste
the
> names together and then use them as an object references.
Yes.

The get() and assign() functions allow you to reference objects by
character strings, and as.name() will convert a string into a reference
(you would then probably need to use substitute() to create an expression
and eval()) to evaluate it.

eg

    assign("a",get("b"))
does
    a<-b


Often there is a better way: the objects can be stored in a list, making
it possible to use character strings directly to reference them

If  obj<-list(a=1,b=2)

then obj[["a"]] is a reference to the "a" element and you
can do eg

obj[["a"]]<-otherobj[["b"]]


	-thomas

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> Is there a function to convert character strings to object
> references.  For example, I want to name sets of objects
> based on scenarios and the types of data being stored.
> So the scenarios might be something like c("a", "b",
> "c"), the types of data might have names like
c("pass.trp",
> "trk.trp", "cmute.trp"), and I want to assign data to
the
> objects a.pass.trp, b.pass.trp, c.pass.trp, a.trk.trp, etc.
> I'd like to be able to paste the names together and then
> use them as an object references.
For example,

obj <- eval (parse (text=paste ("a", "pass.trp",
sep="")))


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?assign

GP
> Is there a function to convert character strings to object references.  For
> example, I want to name sets of objects based on scenarios and the types of
> data being stored.  So the scenarios might be something like
c("a", "b",
> "c"), the types of data might have names like
c("pass.trp", "trk.trp",
> "cmute.trp"), and I want to assign data to the objects
a.pass.trp,
> b.pass.trp, c.pass.trp, a.trk.trp, etc.  I'd like to be able to paste
the
> names together and then use them as an object references.
> 
> Brian Gregor, P.E.
> Transportation Planning Analysis Unit
> Oregon Department of Transportation
> Brian.J.GREGOR at odot.state.or.us
> (503) 986-4120
-- 

 __________________________________________________
[                                                  ]
[ Giovanni Petris                 GPetris at uark.edu ]
[ Department of Mathematical Sciences              ]
[ University of Arkansas - Fayetteville, AR 72701  ]
[ Ph: (479) 575-6324, 575-8630 (fax)               ]
[ http://definetti.uark.edu/~gpetris/              ]
[__________________________________________________]

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