eval and as.name

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?

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