Hi Rolf, Barry,
On 03/04/2014 08:08 AM, Barry Rowlingson wrote:
On Tue, Mar 4, 2014 at 1:47 AM, Rolf Turner <r.tur...@auckland.ac.nz> wrote:
Questions:
==========
(2) Even if there are no such functions, is there anything intrinsically
*wrong* with having a function possessing this somewhat schizophrenic
nature? Is it likely to cause confusion, induce syntactical mistakes,
create errors, or produce wrong results?
Any thoughts, comments, insights or suggestions gratefully received.
I don't see why you can't conceptually think of w = owin(some_ppp_object)
as an owin "Constructor" rather than an "Accessor". Its "constructing" (and
returning) an owin from an object, it just happens to be as simple as
getting a component from that object.
The raster package has the 'extent' function - you can create an extent
with extent(xmin,xmax,,,etc), get the extent of a raster with extent(r), or
set the extent of a raster with extent(r1) <- extent(r2), so I don't see
any problem with:
w1 = owin(poly=...) # construct polygon owin
ppp1 = ppp(x,y,window=w1)
ppp2 = ppp(x,y, window=owin(ppp1)) # construct window from ppp object
owin(ppp1) = owin(ppp2) # give ppp1 the owin of ppp2
That all reads pretty nicely. As long as owin(...) returns an observation
window and owin<-(...) assigns an observation window to an object that can
validly have one, I don't think you can go wrong. I've probably already
tried to do "owin(ppp1)=..." a few times...
I agree with Barry. Once you realize there is no clear line between
constructor and extractor (conceptually every function can actually
be thought of as a constructor), then re-using the same function name
(via methods of a generic function) doesn't sound too bad. An example
of this design is the strand() generic in Bioconductor: can be used
to get or set the strand factor of an object containing such a
component (e.g. a GRanges object), and also for constructing a
strand factor from different kinds of input (character, logical,
integer vector, etc...)
Cheers,
H.
Barry
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