Force evaluation of a symbol when a function is created
Here's one more way. It seems to me this is the most R-like way to do
what you want:
multiply_by_Y <- function(Y) {
force(Y)
function(x) x*Y
}
F <- multiply_by_Y(3)
The "force" call forces Y to be evaluated at that point, so its value is
fixed from that point forward.
Duncan Murdoch
On 12-08-06 5:07 PM, Schoenfeld, David Alan,Ph.D.,Biostatistics wrote:
I am porting a program in matlab to R,
The problem is that Matlab has a feature where symbols that aren't arguments are evaluated immediately.
That is:
Y=3
F=@(x) x*Y
Will yield a function such that F(2)=6.
If later say. Y=4 then F(2) will still equal 6.
R on the other hand has lazy evaluation.
F<-function(x){x*Y}
Will do the following
Y=3
F(2)=6
Y=4
F(2)=8.
Does anyone know of away to defeat lazy evaluation in R so that I can easily simulate the Matlab behavior. I know that I can live without this in ordinary programming but it would make my port much easier.
Thanks.
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