[R] binding vectors or matrix using their names

[Bill.Venables@csiro.au]

Goodness Patrick, this must surely qualify for the obfuscated R competition finals.  I love it!

There are two solutions I can think of with do.call and here they are:

> x <- 1
> x2 <- runif(10)
> x12 <- c("x", "x2")

> do.call("cbind", lapply(x12, as.name))
      x         x2
 [1,] 1 0.99327265
 [2,] 1 0.63260097
 [3,] 1 0.17411170
 [4,] 1 0.54635634
 [5,] 1 0.75603670
 [6,] 1 0.27739270
 [7,] 1 0.32125068
 [8,] 1 0.01326344
 [9,] 1 0.37519602
[10,] 1 0.11133052

> do.call("cbind", lapply(x12, get))
      [,1]       [,2]
 [1,]    1 0.99327265
 [2,]    1 0.63260097
 [3,]    1 0.17411170
 [4,]    1 0.54635634
 [5,]    1 0.75603670
 [6,]    1 0.27739270
 [7,]    1 0.32125068
 [8,]    1 0.01326344
 [9,]    1 0.37519602
[10,]    1 0.11133052
> 

I suspect the first offers a few advantages over the second, (which some other people have implicitly suggested).  The first preserves the names in the result.  Also, if the vectors are large, the second constructs a large language object and then evaluates it to get a large result.  The first uses the names rather than the objects themselves, so at least the language object is small, even if the result is not.

A more serious, philosophical word on Patrick's solution.  It is rarely necessary (in my limited experience, sure) to have to use parse() like this.  Where it provides a quick (kludgy?) solution I often find it a useful exercise to consider alternatives.  They often come out simpler and you nearly always pick up something useful in the process.

Bill V.



-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Patrick Burns
Sent: Thursday, 25 March 2004 7:02 AM
To: Stephane DRAY
Cc: r-help at stat.math.ethz.ch; Stephane DRAY; Tom Blackwell
Subject: Re: [R] binding vectors or matrix using their names


I think you are looking for the eval-parse-text idiom:

eval(parse(text=paste("cbind(", paste(my.names, collapse=", "), ")")))

Patrick Burns

Burns Statistics
patrick at burns-stat.com
+44 (0)20 8525 0696
http://www.burns-stat.com
(home of S Poetry and "A Guide for the Unwilling S User")

Stephane DRAY wrote:

> Hi Tom,
>
> Your approach did not work,
>
> > do.call("cbind", as.list(my.names))
>      [,1] [,2]
> [1,] "x"  "x2"
>
> but it helps me a lot to find the good one:
>
> do.call("cbind", as.list(parse(text=my.names)))
>
> Thanks,
>
>
> At 14:56 24/03/2004, Tom Blackwell wrote:
>
>> I believe the syntax is
>>
>> result <- do.call(cbind, as.list(my.names))
>>
>> Haven't checked this on your example, though.
>>
>> -  tom blackwell  -  u michigan medical school  -  ann arbor  -
>>
>> On Wed, 24 Mar 2004, Stephane DRAY wrote:
>>
>> > Hello list,
>> > I have two vectors x and x2:
>> >
>> > x=runif(10)
>> > x2=runif(10)
>> >
>> > and one vectors with their names :
>> >
>> > my.names=c("x","x2")
>> >
>> > I would like to cbind these two vectors using their names contained
>> in the
>> > vector my.names.
>> > I can create a string with comma
>> > ncomma=paste(my.names,collapse=",")
>> >
>> > and now, I just need a function to transform this string into a
>> adequate
>> > argument for cbind:
>> >
>> > cbind(afunction(ncomma))
>> >
>> > Is there in R a function that can do the job ? If not, how can I do
>> it ??
>> >
>> > Thanks in advance,
>> > Sincerely.
>> >
>> >
>> > Stéphane DRAY
>> > 
>> ---------------------------------------------------------------------
>> -----------------------------
>>
>> >
>> > Département des Sciences Biologiques
>> > Université de Montréal, C.P. 6128, succursale centre-ville 
>> > Montréal, Québec H3C 3J7, Canada
>> >
>> > Tel : 514 343 6111 poste 1233
>> > E-mail : stephane.dray at umontreal.ca
>> > 
>> ---------------------------------------------------------------------
>> -----------------------------
>>
>> >
>> > Web                                          
>> http://www.steph280.freesurf.fr/
>> >
>> > ______________________________________________
>> > R-help at stat.math.ethz.ch mailing list 
>> > https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>> > PLEASE do read the posting guide!
>> http://www.R-project.org/posting-guide.html
>> >
>>
>> ______________________________________________
>> R-help at stat.math.ethz.ch mailing list 
>> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide!
>> http://www.R-project.org/posting-guide.html
>
>
> Stéphane DRAY
> ----------------------------------------------------------------------
> ----------------------------
>
> Département des Sciences Biologiques
> Université de Montréal, C.P. 6128, succursale centre-ville Montréal, 
> Québec H3C 3J7, Canada
>
> Tel : 514 343 6111 poste 1233
> E-mail : stephane.dray at umontreal.ca
> ----------------------------------------------------------------------
> ----------------------------
>
> Web                                          
> http://www.steph280.freesurf.fr/
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list 
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
>
>

______________________________________________
R-help at stat.math.ethz.ch mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html