On Aug 7, 2011, at 21:25 , Carl Witthoft wrote:
> Just chiming in here...
>
> Granted some of the help files are a bit cryptic until you get used to them
> (but still much easier to understand than the Unix man pages :-) ). This
> sort of thing does provide a chance to learn about the power of R.
>
> From Rolf's example, suppose that integrate() did NOT have any additional
> arguments. Then, do this:
>
> bar <- function(x) foo(x,y=pi/4)
>
> integrate(bar, 0, 2*pi)
>
>
> As an exercise to the reader :-) , write a function which takes an input for
> the value of y and uses some subset of "paste, eval, do.call, parse" etc., to
> build the function bar() on the fly.
>
> fortune("rethink")
If the answer is parse() you should usually rethink the question.
-- Thomas Lumley
R-help (February 2005)
To programmatically define the body of a function, consider something like
body(bar) <- bquote(foo(x,y=.(y)))
but actually plain old lexical scoping does the trick
> g <- function(y) {
+ foo <- function(x){sin(x^2 + y^2)}
+ integrate(foo,0,2*pi)
+ }
> g(pi/4)
0.9314315 with absolute error < 1.5e-05
> g(pi/3)
0.920137 with absolute error < 2.7e-05
> g(pi/8)
0.7427584 with absolute error < 8.3e-06
as does various other varations over the "unbound variable" theme, e.g.
> f <- local(function(x){sin(x^2 + y^2)})
> g <- function(y) {
+ assign("y", y, environment(f))
+ integrate(f, 0, 2*pi)
+ }
> g(pi/8)
0.7427584 with absolute error < 8.3e-06
> Carl
>
>
> <quote>
> From: Rolf Turner <rolf.turner_at_xtra.co.nz>
> Date: Sat, 06 Aug 2011 11:00:11 +1200
> On 06/08/11 08:17, brunero liseo wrote:
> > Is it possible to use the "integrate" function when it depends on a
> > parameter?
> > in other words can i get something like
> >
> > f(y) = integrate (g(x,y))?
> > If not, how else can I get that?
> > thanks in advance
> This really boils down to ``RTFM''.
>
> The help for "integrate" ``clearly'' ( :-) ) states that there is a "..."
> argument
> which consists of ``additional arguments passed to f''. So use it.
>
> E.g.:
>
> foo <- function(x,y){sin(x^2 + y^2)}
> integrate(foo,0,2*pi,y=pi/4)
> 0.9314315 with absolute error < 1.5e-05
>
> Most of the time, what you need to know is in the help. You just need to
> learn to read the help *carefully* and think along the lines: ``This *does*
> mean something useful and is actually expressed in a rational albeit it
> cryptic manner. Given that fact, what could this *possibly* mean?''
> That will usually get you there. Then *try* what you think you gleaned from
> the help using a *simple* example.
>
> cheers,
>
> Rolf Turner
> </quote>
> --
> -----
> Sent from my Cray XK6
>
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--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd....@cbs.dk Priv: pda...@gmail.com
"Døden skal tape!" --- Nordahl Grieg
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