I have a vector of character strings that look like R expressions:
> a <- paste("qss(",paste("x",1:6,sep = "")
,", lambda =100)", sep =
"")
> a
[1] "qss(x1, lambda =100)" "qss(x2, lambda =100)"
"qss(x3, lambda =100)"
[4] "qss(x4, lambda =100)" "qss(x5, lambda =100)"
"qss(x6, lambda =100)"
That I would like to operate on to obtain the names of the first
argument, i.e.
> foo(a)
[1] "x1" "x2" "x3" "x4" "x5"
"x6"
I thought there was some simple idiom involving deparse, but it is
eluding
my searches.
url: www.econ.uiuc.edu/~roger Roger Koenker
email rkoenker at uiuc.edu Department of Economics
vox: 217-333-4558 University of Illinois
fax: 217-244-6678 Champaign, IL 61820
unlist(lapply(parse(text=a), function(x) deparse(x[[2]]))) seems to do the job. Patrick Burns patrick at burns-stat.com +44 (0)20 8525 0696 http://www.burns-stat.com (home of "The R Inferno" and "A Guide for the Unwilling S User") roger koenker wrote:> I have a vector of character strings that look like R expressions: > > > a <- paste("qss(",paste("x",1:6,sep = "") ,", lambda =100)", sep = "") > > a > [1] "qss(x1, lambda =100)" "qss(x2, lambda =100)" "qss(x3, lambda =100)" > [4] "qss(x4, lambda =100)" "qss(x5, lambda =100)" "qss(x6, lambda =100)" > > That I would like to operate on to obtain the names of the first > argument, i.e. > > > foo(a) > [1] "x1" "x2" "x3" "x4" "x5" "x6" > > I thought there was some simple idiom involving deparse, but it is > eluding > my searches. > > > url: www.econ.uiuc.edu/~roger Roger Koenker > email rkoenker at uiuc.edu Department of Economics > vox: 217-333-4558 University of Illinois > fax: 217-244-6678 Champaign, IL 61820 > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > >
one way seems to be the following:
a <- paste("qss(",paste("x",1:6,sep = "")
,", lambda =100)", sep = "")
all.vars(parse(text = a))
I hope it helps.
Best,
Dimitris
roger koenker wrote:> I have a vector of character strings that look like R expressions:
>
> > a <- paste("qss(",paste("x",1:6,sep =
"") ,", lambda =100)", sep = "")
> > a
> [1] "qss(x1, lambda =100)" "qss(x2, lambda =100)"
"qss(x3, lambda =100)"
> [4] "qss(x4, lambda =100)" "qss(x5, lambda =100)"
"qss(x6, lambda =100)"
>
> That I would like to operate on to obtain the names of the first
> argument, i.e.
>
> > foo(a)
> [1] "x1" "x2" "x3" "x4"
"x5" "x6"
>
> I thought there was some simple idiom involving deparse, but it is eluding
> my searches.
>
>
> url: www.econ.uiuc.edu/~roger Roger Koenker
> email rkoenker at uiuc.edu Department of Economics
> vox: 217-333-4558 University of Illinois
> fax: 217-244-6678 Champaign, IL 61820
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center
Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
a1 <- "qss(x1,lambda=100)"> parse(text=a1)[[1]][[2]]x1 This will not work for length(a) != 1, so you have to explicitly map over your list, e.g. a <- paste("qss(",paste("x",1:6,sep = "") ,", lambda =100)", sep = "")> dput( lapply(a,function(x)parse(text=x)[[1]][[2]]) )list(x1, x2, x3, x4, x5, x6) paste(lapply(a,function(x)parse(text=x)[[1]][[2]]),collapse=", ") [1] "x1, x2, x3, x4, x5, x6" -s On Tue, Apr 7, 2009 at 3:26 PM, roger koenker <rkoenker at uiuc.edu> wrote:> I have a vector of character strings that look like R expressions: > >> a <- paste("qss(",paste("x",1:6,sep = "") ,", lambda =100)", sep = "") >> a > [1] "qss(x1, lambda =100)" "qss(x2, lambda =100)" "qss(x3, lambda =100)" > [4] "qss(x4, lambda =100)" "qss(x5, lambda =100)" "qss(x6, lambda =100)" > > That I would like to operate on to obtain the names of the first argument, > i.e. > >> foo(a) > [1] "x1" "x2" "x3" "x4" "x5" "x6" > > I thought there was some simple idiom involving deparse, but it is eluding > my searches. > > > url: ? ?www.econ.uiuc.edu/~roger ? ? ? ? ? ?Roger Koenker > email ? ?rkoenker at uiuc.edu ? ? ? ? ? ?Department of Economics > vox: ? ? 217-333-4558 ? ? ? ? ? ? ? ?University of Illinois > fax: ? ? ? 217-244-6678 ? ? ? ? ? ? ? ?Champaign, IL 61820 > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >