[R] Access and assign list sub-elements using a string suchas "l$a$b"

[Dimitris Rizopoulos]

----- Original Message ----- 
From: "Petr Pikal" <petr.pikal at precheza.cz>
To: "Gregory Jefferis" <gsxej2 at cam.ac.uk>
Cc: <r-help at stat.math.ethz.ch>
Sent: Thursday, June 15, 2006 4:56 PM
Subject: Re: [R] Access and assign list sub-elements using a string 
suchas "l$a$b"


> Hi
> very, very close
>
>
> On 15 Jun 2006 at 13:27, Gregory Jefferis wrote:
>
> Date sent:      Thu, 15 Jun 2006 13:27:05 +0100
> From:           Gregory Jefferis <gsxej2 at cam.ac.uk>
> To:             "r-help-request at stat.math.ethz.ch" 
> <r-help-request at stat.math.ethz.ch>
> Forwarded to:   <r-help at stat.math.ethz.ch>
> Forwarded by:   Gregory Jefferis <gsxej2 at cam.ac.uk>
> Date forwarded: Thu, 15 Jun 2006 14:54:13 +0100
> Subject:        [R] Access and assign list sub-elements using a 
> string such as
> "l$a$b"
>
>> If I have a list I can set a sub-element as follows on the command
>> line:
>>
>> people=list()
>> people$tom$hair="brown"
>> people
>>
>> But what if I have a string containing the name of the sub-element
>> that I want to access?
>>
>> subel= "people$tom$hair"
>>
>> get(subel) # returns error
>> assign(subel,"red") # silent but doesn't change list
>> people
>
> See what happens when
>
> people<-assign(subel, "red")

but I think this is not what Greg wanted; the above just assigns "red" 
to object 'people' (i.e., check `str(assign(subel, "red"))'). If I 
understood correctly, the following could be of help:

people <- list()
people$tom$hair <- "brown"
people
#################
subel <- "people$tom$hair"
eval(parse(text = subel))
eval(parse(text = paste(subel, "<- 'red'")))
people


Best,
Dimitris


----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
     http://www.student.kuleuven.be/~m0390867/dimitris.htm


> HTH
> Petr
>
>
>>
>> The attempts above using assign/get won't do what I am trying to do
>> [nor according to the help should they].  I would be very grateful 
>> for
>> any suggestions.  Many thanks,
>>
>> Greg.
>>
>> -- 
>> Gregory Jefferis, PhD                                   and:
>> Research Fellow
>> Department of Zoology                                   St John's
>> College University of Cambridge
>> Cambridge Downing Street                                   CB2 1TP
>> Cambridge, CB2 3EJ United Kingdom
>>
>> Lab Tel: +44 (0)1223 336683                     Office: +44 (0)1223
>> 339899 Lab Fax: +44 (0)1223 336676
>>
>> http://www.zoo.cam.ac.uk/zoostaff/jefferis.html
>> gsxej2 at cam.ac.uk
>>
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>
> Petr Pikal
> petr.pikal at precheza.cz
>
> ______________________________________________
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