[R] evaluating the contents of a string

[David A Richmond]

On Mon, 1 Oct 2001, Thomas Lumley wrote:
> In general, this sort of question is frequently a sign that someone is
> doing things the hard way.  There are some real situations where you need
> to operate on strings like this, but they are fairly rare.

Well, actually I don't know if I'm reinventing the wheel here, but my
objective was to write a function which lists the objects in memory with
characteristic info, like data type, dimensions, and memory used. so I use
ls(pos=1) to get the list of objects at the 'root' level, and then use
get(i,pos=1) to get information about each object, then display it in a
table. It works nicely with get, and I can make it available if anyone's
interested. (I call it "describe" and it displays the name, type,
dimensions and size of each object)

dave richmond


On Mon, 1 Oct 2001, Thomas Lumley wrote:

> On Fri, 28 Sep 2001, David A Richmond wrote:
> <snip>
> > is there a function to pass bname to such that dim returns the dimensions
> > of b?
> <snip>
>
> As already pointed out, eval(parse(text=bname)) will return the object
> whose name is in the text string. Another way is get(bname), which is more
> specific (it gets objects by name, rather than evaluating arbitrary code).
> 
> In general, this sort of question is frequently a sign that someone is
> doing things the hard way.  There are some real situations where you need
> to operate on strings like this, but they are fairly rare.
> 
> For example, if you have a collection of arrays and may want the
> dimensions of any one of them, you could put them in a list
> 
> 
>  listofarrays<-list()
>  listofarrays$b <- matrix(1:9,3,3)
>  dim(listofarrays$b)
> 
> and even
>  bname<-"b"
>  dim(listofarrays[[bname]])
> 
> 
> 	-thomas
> 
> Thomas Lumley			Asst. Professor, Biostatistics
> tlumley at u.washington.edu	University of Washington, Seattle
> 
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|David Richmond                It works on a          |      
+ Dept. of Sociology          complex scientific      + 
|Saint Mary's College          principle, known as    |  
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