On 11/15/12 9:22 AM, Ted Dunning wrote: > On Thu, Nov 15, 2012 at 8:42 AM, Phil Steitz <phil.ste...@gmail.com> wrote: > >> On 11/15/12 8:01 AM, Ted Dunning wrote: >>> The typical answer to this when adding a functional method like compute >> is to also add a view object. The rationale is that a small number of view >> methods can be composed with a small number of compute/aggregate methods to >> get the expressive power of what would otherwise require a vast array of >> methods. >> >> If I understand correctly, we already have a view object exposed - >> getElements. The challenge is that this method returns a copy and >> what we would like is a way to get a function computed directly on >> the data encapsulated in the RDA. Without function pointers or real >> array references, I don't see a straightforward way to do this. >> >> > When I say view, I mean something that is a reference and is not a copy. > The getElements method is a copy, not view under this terminology.
Do you know how to do that with a primitive array? Can you provide some sample code? Thanks for your help on this. Phil > > The Colt/Mahout approach is to define a view object which opaquely > remembers a reference to the original, an offset and a length. Functions > and other arguments can be passed to this view object which operates on a > subset of the original contents by calling the function. Performance is > actually quite good. The JIT seems to in-line the view object access to > the underlying object and also in-lines evaluation of the function so that > the actual code that is executed is pretty much what you would write in C, > but you don't have to worry as much since the pattern of access is more > controlled. > > For completeness, this is essentially what java.nio does with the *Buffer > classes as well. You can wrap an array and then you can ask for slices out > of that array while retaining the reference semantics. > --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
