Jake Mannix created MAHOUT-1227:
-----------------------------------
Summary: Vector.iterateNonZero() is super-clumsy to use: add
Iterable<Element> allNonZero()
Key: MAHOUT-1227
URL: https://issues.apache.org/jira/browse/MAHOUT-1227
Project: Mahout
Issue Type: Improvement
Environment: all
Reporter: Andy Schlaikjer
Assignee: Jake Mannix
Fix For: 0.8
Currently, our codebase is littered with the following:
[code]
Iterator<Element> it = vector.iterateNonZero();
while (it.hasNext()) {
Element e = it.next();
...
[code]
wouldn't it be nice to be able to do:
[code]
for (Element e : vector.allNonZero()) {
...
[code]
instead?
I propose adding an Iterable<Element> allNonZero() which allow this syntactic
sugar. To make it symmetric with iterateAll, let's also add Iterable<Element>
all(), and implement the simply in AbstractVector.
The first diff adding this is very non-invasive - new methods added to
interface, implemented in the three classes from which all Vector
implementations derive (AbstractVector, NamedVector, and DelegatingVector).
User code should just work, unless they've implemented their own vector without
subclassing one of these three (yikes).
Next diff, which is more invasive, would remove "extends Iterable<Element>"
from Vector, because using the foreach of a Vector itself is very rarely what
the caller really means to do (it's the all-iterator, very bad for the more
common sparse use case). To achieve the same effect, the caller chooses
between vector.all() and vector.allNonZero(), and then they're being crystal
clear what they mean.
Lastly, I'd propose we make iterateAll() and iterateAllNonZero() protected
methods on AbstractVector, so that we are forced to remove all the clumsy
places where we do Iterator<Element> it = ... all throughout the codebase. I
suspect there will be very few places left that really want the raw iterator,
but if there are any, it can be gotten by calling
vector.(all/allNonZero).iterator()
(feature-request/api fix suggestion idea courtesy of Andy Schlaikjer,
formalized as a proposal and posted up here by me, Jake Mannix)
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