R help - Jan 2010 - evaluating expressions with sub expressions

Hallo

I'm having trouble figuring out how to evaluate an expression when one of
the variables in the expression is defined separately as a sub expression.
Here's a simplified example

mat <- expression(0, f1*s1*g1)  # vector of formulae
g1 <- expression(1/Tm)          # expansion of the definition of g1
vals <- data.frame(f1=1, s1=.5, Tm=2) # one set of possible values for
variables

before adding this sub expression I was using the following to evaluate
"mat"

sapply(mat, eval, vals)

Obviously I could manually substitute in 1/Tm for each g1 in the
definition of "mat", but the actual expression vector is much longer,
and
the sub expression more complicated. Also, the subexpression is often
adjusted for different scenarios.  Is there a simple way of changing this
or redefining "mat" so that I can define "g1" like a macro
to be used in
the expression vector.

Thanks!
Jennifer

Hi,

Would this do as an alternative syntax?

g1 <- quote(1/Tm)
mat <- list(0, bquote(f1*s1*.(g1)))
vals <- data.frame(f1=1, s1=.5, Tm=2)

sapply(mat, eval, vals)

HTH,

baptiste


On 29 January 2010 17:51, Jennifer Young
<Jennifer.Young at math.mcmaster.ca> wrote:
> Hallo
>
> I'm having trouble figuring out how to evaluate an expression when one
of
> the variables in the expression is defined separately as a sub expression.
> Here's a simplified example
>
> mat <- expression(0, f1*s1*g1) ?# vector of formulae
> g1 <- expression(1/Tm) ? ? ? ? ?# expansion of the definition of g1
> vals <- data.frame(f1=1, s1=.5, Tm=2) # one set of possible values for
> variables
>
> before adding this sub expression I was using the following to evaluate
"mat"
>
> sapply(mat, eval, vals)
>
> Obviously I could manually substitute in 1/Tm for each g1 in the
> definition of "mat", but the actual expression vector is much
longer, and
> the sub expression more complicated. Also, the subexpression is often
> adjusted for different scenarios. ?Is there a simple way of changing this
> or redefining "mat" so that I can define "g1" like a
macro to be used in
> the expression vector.
>
> Thanks!
> Jennifer
>
> ______________________________________________
> 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.
>

The following recursively walks the expression tree.  The esub
function is from this page (you may wish to read that entire thread):
http://tolstoy.newcastle.edu.au/R/help/04/03/1245.html

esub <- function(expr, sublist) do.call("substitute", list(expr,
sublist))

proc <- function(e, env = parent.frame()) {
   for(nm in all.vars(e)) {
      if (exists(nm, env) && is.language(g <- get(nm, env))) {
         if (is.expression(g)) g <- g[[1]]
            g <- Recall(g, env)
            L <- list(g)
            names(L) <- nm
             e <- esub(e, L)
	  }
        }
     e
}

mat <- expression(0, f1*s1*g1)
g1 <- expression(1/Tm)
vals <- data.frame(f1=1, s1=.5, Tm=2)
e <- sapply(mat, proc)
sapply(e, eval, vals)

The last line should give:
> sapply(e, eval, vals)
[1] 0.00 0.25


On Fri, Jan 29, 2010 at 11:51 AM, Jennifer Young
<Jennifer.Young at math.mcmaster.ca> wrote:
> Hallo
>
> I'm having trouble figuring out how to evaluate an expression when one
of
> the variables in the expression is defined separately as a sub expression.
> Here's a simplified example
>
> mat <- expression(0, f1*s1*g1) ?# vector of formulae
> g1 <- expression(1/Tm) ? ? ? ? ?# expansion of the definition of g1
> vals <- data.frame(f1=1, s1=.5, Tm=2) # one set of possible values for
> variables
>
> before adding this sub expression I was using the following to evaluate
"mat"
>
> sapply(mat, eval, vals)
>
> Obviously I could manually substitute in 1/Tm for each g1 in the
> definition of "mat", but the actual expression vector is much
longer, and
> the sub expression more complicated. Also, the subexpression is often
> adjusted for different scenarios. ?Is there a simple way of changing this
> or redefining "mat" so that I can define "g1" like a
macro to be used in
> the expression vector.
>
> Thanks!
> Jennifer
>
> ______________________________________________
> 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.
>