[R] how to get a value from a list (using paste function)?

[William Dunlap]

> Can you please elaborate. What are the negatives about the method

Here are a few examples of eval(parse(text=paste())) failing:
  > cvtest <- list("Test-1"=1, Bozo=2, "Joe's Test"=3)
  >
  > lambda.rule <- "Test-1"
  > eval(parse(text=paste0("cvtest$", lambda.rule))) # want 1
  [1] 0
  > 
  > lambda.rule <- "Joe's Test"
  > eval(parse(text=paste0("cvtest$", lambda.rule))) # want 3
  Error in parse(text = paste0("cvtest$", lambda.rule)) : 
    <text>:1:11: unexpected INCOMPLETE_STRING
  1: cvtest$Joe's Test
             ^

and here is an example of "$" giving a suboptimal result:
  > cvtest$B # want NULL (there is no component named "B")
  [1] 2

"[[" gives the correct result in all cases:
  > lambda.rule <- "Test-1"
  > cvtest[[lambda.rule]]
  [1] 1
  > lambda.rule <- "B"
  > cvtest[[lambda.rule]]
  NULL
  > lambda.rule <- "Bozo"
  > cvtest[[lambda.rule]]
  [1] 2
  > lambda.rule <- "Joe's Test"
  > cvtest[[lambda.rule]]
  [1] 3

Also, I find it hard to read code involving eval(parse(text=paste(...))).

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Heramb Gadgil
> Sent: Thursday, December 27, 2012 2:44 AM
> To: Uwe Ligges
> Cc: Thomas Stewart; r-help
> Subject: Re: [R] how to get a value from a list (using paste function)?
> 
> I am not sure why "Never ever!"
> 
> Can you please elaborate. What are the negatives about the method
> 
> Warm Regards,
> Heramb M. Gadgil
> 
> 
> On Thu, Dec 27, 2012 at 3:50 PM, Uwe Ligges <ligges at statistik.tu-dortmund.de
> > wrote:
> 
> >
> >
> > On 27.12.2012 08:09, Heramb Gadgil wrote:
> 
> >> eval(parse(text=paste0("**cvtest$",lambda.rule)))
> >>
> >
> > No, never ever!
> >
> > There is an R idiom made for it:
> >
> > cvtest[[lambda.rule]]
> >
> > Uwe Ligges
> >
> >
> >
> >
> >
> >
> >
> >  I hope this works.
> >>
> >> On Wed, Dec 19, 2012 at 12:57 AM, Thomas Stewart
> >> <tgs.public.mail at gmail.com>**wrote:
> >>
> >>  Soyeon-
> >>>
> >>> A possible solution:
> >>>
> >>> get(lambda.rule,envir=**list2env(cvtest))
> >>>
> >>>
> >>> On Tue, Dec 18, 2012 at 12:34 PM, Soyeon Kim <yunni0731 at gmail.com>
> >>> wrote:
> >>>
> >>>  Dear my R friends,
> >>>>
> >>>> I want to get a number from a list using paste function.
> >>>> In my example,
> >>>> lambda.rule <- "lambda.1se"
> >>>> cvtest is a list (result from cv.glmnet)
> >>>> and
> >>>> cvtest$lambda.1se
> >>>> [1] 1.308973
> >>>>
> >>>> I want to call the value using paste function.
> >>>> I used get function but there was an error.
> >>>> test <-  get(paste("cvtest$",lambda.**rule, sep=""))
> >>>> Error in get(paste("cvtest$", lambda.rule, sep = "")) :
> >>>>    object 'cvtest$lambda.1se' not found
> >>>>
> >>>> Do you guys know how to solve this issue?
> >>>>
> >>>> Thank you so much in advance and merry Christmas!
> >>>>
> >>>> Soyeon
> >>>>
> >>>> ______________________________**________________
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> >>>> and provide commented, minimal, self-contained, reproducible code.
> >>>>
> >>>>
> >>>>
> >>>>
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> >>> ______________________________**________________
> >>> R-help at r-project.org mailing list
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