Paulo Grahl wrote:
Dear All:
I have a question regarding the behavior of functions.
Say I define a function that returns another function :
A <- function(parameters) {
# calculations w/ parameters returning 'y'
tmpf <- function(x) { # function of 'y' }
return(tmpf)
}
The value of the parameters are stored in an environment local to the
function. Then I call
x<- something
B<-A(x)
When R executes this last statement, does it perform all the
calculations inside function A again
no, see this:
> f <- function( x = 3){
+ function( ){}
+ }
> g <- f()
> ls.str( environment(g) )
x : num 3
> h <- f(6)
> ls.str( environment(h) )
x : num 6
> ls.str( environment(g) )
x : num 3
See also colorRampPalette which uses this feature:
> colorRampPalette
function (colors, ...)
{
ramp <- colorRamp(colors, ...)
function(n) {
x <- ramp(seq.int(0, 1, length.out = n))
rgb(x[, 1], x[, 2], x[, 3], maxColorValue = 255)
}
}
<environment: namespace:grDevices>
> pal <- colorRampPalette( c("blue", "white", "red") )
> pal
function (n)
{
x <- ramp(seq.int(0, 1, length.out = n))
rgb(x[, 1], x[, 2], x[, 3], maxColorValue = 255)
}
<environment: 0x99aba4c>
> ls.str( environment( pal ) )
colors : chr [1:3] "blue" "white" "red"
ramp : function (x)
(i.e., all the calculations that
yield 'y')
or the value of 'y' is already stored in the function's local environment ?
Many thanks.
Paulo Gustavo Grahl, CFA
--
Romain Francois
Independent R Consultant
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
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