I'm sure there is a more general way to ask this question but how do
you use the elements of a character vector as names of objects in an
expression?
For example, say you have:
a = c(1,3,5,7)
b = c(2,4,6,8)
n=c("a","b")
and you want to use the names a and b in a function (e.g. sum)
sum(eval(as.name(n[1])),eval(as.name(n[2])))
works but
what is a simpler way to effect this level of indirection?
I am new to R, so maybe I'm missing the point of your question. But why wouldn't you just use sum(a,b)? Murray M Cooper, Ph.D. Richland Statistics 9800 N 24th St Richland, MI, USA 49083 Mail: richstat at earthlink.net ----- Original Message ----- From: "Fuchs Ira" <irafuchs at gmail.com> To: <r-help at r-project.org> Sent: Thursday, February 05, 2009 5:10 PM Subject: [R] eval and as.name> I'm sure there is a more general way to ask this question but how do you > use the elements of a character vector as names of objects in an > expression? > For example, say you have: > > a = c(1,3,5,7) > b = c(2,4,6,8) > > n=c("a","b") > > and you want to use the names a and b in a function (e.g. sum) > > sum(eval(as.name(n[1])),eval(as.name(n[2]))) > > works but > > what is a simpler way to effect this level of indirection? > > ______________________________________________ > 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. >
Fuchs Ira wrote:> I'm sure there is a more general way to ask this question but how do > you use the elements of a character vector as names of objects in an > expression? > For example, say you have: > > a = c(1,3,5,7) > b = c(2,4,6,8) > > n=c("a","b") > > and you want to use the names a and b in a function (e.g. sum) > > sum(eval(as.name(n[1])),eval(as.name(n[2]))) > > works but > > what is a simpler way to effect this level of indirection? >in this particular case, the simplest i can come up with is: sum(sapply(n, get)) you may want to avoid this sort of indirection by using lists with named components: d = list(a=c(1,3,5,7), b=c(2,4,6,8)) sum(unlist(d)) with(d, sum(a+b)) sum(d[['a']], d[['b']]) sum(sapply(n, function(v) d[[v]])) and so on. vQ
These are all great resposes but I think I should have given a
slightly more complete description of the problem.
I am using the quantmod package and I have called getSymbols with a
character vector that has a list of stock symbols. For example:
library("quantmod")
list=c("MSFT","AAPL","ORCL")
getSymbols(list)
this returns 3 objects (MSFT,AAPL, ORCL)
now imagine that I want to use the Delt function (also in quantmod) to
calculate the percent difference for each of these stocks using their
closing price.
each closing price is SYMBOL$SYMBOL.Close (can also be retrieved with
Cl(SYMBOL)
I want to construct the call to Delt with the symbols in list appended
with $SYMBOL.Adjusted
in other words I want a way to create
Delt(MSFT$MSFT.Close) merged with Delt(AAPL$AAPL.Close) and so on
(one object having the result of the Delt function for each stock).
I am sure that there are many ways to solve this particular problem.
Perhaps what I need to understand is how to take the characters in the
list and construct an expression and then evaluate the expression.
On Feb 5, 2009, at 5:50 PM, <markleeds@verizon.net> wrote:
> Hi: there's mget but I couldn't figure out how to use it. if you
> figure
> it out, let me know.
> I'm sure one of the guRus will reply with something that uses mget.
> List
> is slow now
> because Europe is sleeping. Good luck.
>
>
>
>
> On Thu, Feb 5, 2009 at 5:42 PM, Ira Fuchs wrote:
>
> > Thanks, that is better but doesn't actually solve my problem which
> is
> > that n is an arbitrary length vector and I'd like to find a way
that
> > avoids having to enumerate the elements of the character vector.
> > Thanks,
> > Ira
> > ----- Original Message -----
> > From: markleeds@verizon.net <markleeds@verizon.net>
> > To: Fuchs Ira <irafuchs@gmail.com>
> > Sent: Thu Feb 05 17:25:39 2009
> > Subject: RE: [R] eval and as.name
> >
> >
> > Hi: below works but it's not much shorter than yours. there must
> be a
> > better way so I'm sending off line in order to encourage better
> > replies.
> >
> > sum(get(n[1]),get(n[2]))
> >
> >
> >
> >
> > On Thu, Feb 5, 2009 at 5:10 PM, Fuchs Ira wrote:
> >
> >> I'm sure there is a more general way to ask this question but
how
> do
> >> you use the elements of a character vector as names of objects in
> an
> >> expression?
> >> For example, say you have:
> >>
> >> a = c(1,3,5,7)
> >> b = c(2,4,6,8)
> >>
> >> n=c("a","b")
> >>
> >> and you want to use the names a and b in a function (e.g. sum)
> >>
> >> sum(eval(as.name(n[1])),eval(as.name(n[2])))
> >>
> >> works but
> >>
> >> what is a simpler way to effect this level of indirection?
> >>
> >> ______________________________________________
> >> R-help@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.
>
[[alternative HTML version deleted]]
VERY nice. That certainly works. Now how does one plot all three variables on one graph? :-) Thanks very much. Ira On Feb 5, 2009, at 7:29 PM, Phil Spector wrote:> Ira - > As you say, there are many ways to solve this problem. > Here's one of them: > > list=c("MSFT","AAPL","ORCL") > getSymbols(list) > > #First, create a function that will take the name of a variable, > #get the Close value from it and pass it to the Delt function: > > makedelt = function(l){now = get(l) ; > Delt(now[,paste(l,".Close",sep='')])} > > #Now create a list of the results from Delt: > > allclose = lapply(list,makedelt) > > #Finally pass the list to Reduce to merge them all together: > > result = Reduce(merge,allclose) > > #To better identify the columns, you can use > > colnames(result) = list > > Hope this helps. > - Phil Spector > Statistical Computing Facility > Department of Statistics > UC Berkeley > spector at stat.berkeley.edu > > > > On Thu, 5 Feb 2009, Fuchs Ira wrote: > >> These are all great resposes but I think I should have given a >> slightly more complete description of the problem. >> >> I am using the quantmod package and I have called getSymbols with a >> character vector that has a list of stock symbols. For example: >> >> library("quantmod") >> list=c("MSFT","AAPL","ORCL") >> getSymbols(list) >> >> this returns 3 objects (MSFT,AAPL, ORCL) >> >> now imagine that I want to use the Delt function (also in quantmod) >> to >> calculate the percent difference for each of these stocks using their >> closing price. >> >> each closing price is SYMBOL$SYMBOL.Close (can also be retrieved with >> Cl(SYMBOL) >> >> I want to construct the call to Delt with the symbols in list >> appended >> with $SYMBOL.Adjusted >> >> in other words I want a way to create >> >> Delt(MSFT$MSFT.Close) merged with Delt(AAPL$AAPL.Close) and so on >> (one object having the result of the Delt function for each stock). >> >> I am sure that there are many ways to solve this particular problem. >> Perhaps what I need to understand is how to take the characters in >> the >> list and construct an expression and then evaluate the expression. >> >> >> On Feb 5, 2009, at 5:50 PM, <markleeds at verizon.net> wrote: >> >>> Hi: there's mget but I couldn't figure out how to use it. if you >>> figure >>> it out, let me know. >>> I'm sure one of the guRus will reply with something that uses mget. >>> List >>> is slow now >>> because Europe is sleeping. Good luck. >>> >>> >>> >>> >>> On Thu, Feb 5, 2009 at 5:42 PM, Ira Fuchs wrote: >>> >>>> Thanks, that is better but doesn't actually solve my problem which >>> is >>>> that n is an arbitrary length vector and I'd like to find a way >>>> that >>>> avoids having to enumerate the elements of the character vector. >>>> Thanks, >>>> Ira >>>> ----- Original Message ----- >>>> From: markleeds at verizon.net <markleeds at verizon.net> >>>> To: Fuchs Ira <irafuchs at gmail.com> >>>> Sent: Thu Feb 05 17:25:39 2009 >>>> Subject: RE: [R] eval and as.name >>>> >>>> >>>> Hi: below works but it's not much shorter than yours. there must >>> be a >>>> better way so I'm sending off line in order to encourage better >>>> replies. >>>> >>>> sum(get(n[1]),get(n[2])) >>>> >>>> >>>> >>>> >>>> On Thu, Feb 5, 2009 at 5:10 PM, Fuchs Ira wrote: >>>> >>>>> I'm sure there is a more general way to ask this question but how >>> do >>>>> you use the elements of a character vector as names of objects in >>> an >>>>> expression? >>>>> For example, say you have: >>>>> >>>>> a = c(1,3,5,7) >>>>> b = c(2,4,6,8) >>>>> >>>>> n=c("a","b") >>>>> >>>>> and you want to use the names a and b in a function (e.g. sum) >>>>> >>>>> sum(eval(as.name(n[1])),eval(as.name(n[2]))) >>>>> >>>>> works but >>>>> >>>>> what is a simpler way to effect this level of indirection? >>>>> >>>>> ______________________________________________ >>>>> 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. >>> >> >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> 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. >>