[R] Using paste to create and evaluate a variable expression

[David Winsemius]

On Sep 16, 2012, at 9:04 PM, Bryan Keller wrote:

> Is it possible to use "paste" to write out an expression and evaluate it?

Of course.

?as.expression
?parse
?eval

> Suppose I want to add two vectors X1 and X2, defined as follows:
> 
> X1 <- 1:6
> X2 <- 6:1
> 
> If I write the following it looks like what I want but is a character:
> noquote(paste(paste("X", 1, sep = ""), paste("X", 2, sep = ""), sep = "+"))

Instead of noquote, you might want to look at bquote.

> 
> Is there a way to tell R that I want to evaluate the text, not just print
> it out as a character?

Evaluate in what context? It looks as though you are building a formula.

parse(text= paste(paste("X", 1, sep = ""), paste("X", 2, sep = ""), sep = "+") )
expression(X1+X2)

-- 
David Winsemius, MD
Alameda, CA, USA