R help - Mar 2001 - Individual rename of list items

I am confused by the logic of renaming:

# Rename individual list items?

Empl<-list(employee="Anna",spouse="Fred")
names(Empl)<-c("empl","spo")
names(Empl)
#[1] "empl" "spo"
# worked like a charm... but

names(Empl[1])<-"newempl"
# no error message, yet ....
names(Empl)
#[1] "empl" "spo"
# where's my newempl???????


If this line

  names(Empl[1])<-"newempl"

was stupid, why is there no error message?

---------------------------------------
Dr. Dieter Menne
Biomed Software
72074 T?bingen
Tel (49) (7071) 52176
FAX (49) (7071) 55 10 46
dieter.menne at menne-biomed.de
www.menne-biomed.de

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> From: "Dieter Menne" <dieter.menne at menne-biomed.de>
> Date: Thu, 1 Mar 2001 12:30:20 +0100
> 
> I am confused by the logic of renaming:
> 
> # Rename individual list items?
> 
> Empl<-list(employee="Anna",spouse="Fred")
> names(Empl)<-c("empl","spo")
> names(Empl)
> #[1] "empl" "spo"
> # worked like a charm... but
> 
> names(Empl[1])<-"newempl"
> # no error message, yet ....
> names(Empl)
> #[1] "empl" "spo"
> # where's my newempl???????
> 
> 
> If this line
> 
>   names(Empl[1])<-"newempl"
> 
> was stupid, why is there no error message?
It wasn't stupid,  but it was not what you intended, evidently.  Look at
> Empl[1]
$employee
[1] "Anna"

That is a list, and you gave it a new name, making a new copy. You did
not then reference the new copy.

What you intended I think was

names(Empl)[1]<-"newempl"

which works, but seems not allowed in the R documentation ....

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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> To: Prof Brian Ripley <ripley at stats.ox.ac.uk>
> Cc: r-help at stat.math.ethz.ch, dieter.menne at menne-biomed.de
> Subject: Re: [R] Individual rename of list items
> From: Peter Dalgaard BSA <p.dalgaard at pubhealth.ku.dk>
> Date: 01 Mar 2001 13:59:32 +0100
> 
> Prof Brian Ripley <ripley at stats.ox.ac.uk> writes:
> 
> > 
> > What you intended I think was
> > 
> > names(Empl)[1]<-"newempl"
> > 
> > which works, but seems not allowed in the R documentation ....
> 
> Er, where? I'd say that one is a consequence of general rules for
> "complex replacements". How well *they* are documented is another
> matter. The R-lang manual has a placeholder consisting of a garbled
> bunch of keywords indicating that someone (me, I'm afraid) at some
> point was going to write something about something like that....
?names says

     `names' is a generic accessor function to the `names' attribute of
     an R object, typically a `vector'. The first form prints the names
     of the observations and the second sets the names. In this case,
     `value' must be a vector of character strings of the same length
     as `x'.

which seems fairly clearly to disallow my example.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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