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https://issues.apache.org/jira/browse/MAHOUT-300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12836238#action_12836238
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Ted Dunning commented on MAHOUT-300:
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{quote}
I dont know what to do in the edge case of vector being negative valued and
sparse. We could return -1 or first index of 0;
{quote}
The rule of thumb is that this should return the same as if you copied the
vector into any other implementation (such as DenseVector) and did the same
operation. Thus 0 is the correct answer.
It may be that someday we will need maxNonZero, but we can do that when it
comes up.
{quote}
An issue i found here was for empty dense vectors
IterateNonZero() optimises for iterating over non zero elements hence result is
still -INF
getNumNonDefaultElements() == size hence it returns -INF instead of zero.
I guess i will have to go with a bool hasNoElements/checkedNoElements based
solution
[ Show ยป ]
Robin Anil added a comment - 20/Feb/10 02:14 PM An issue i found here was for
empty dense vectors IterateNonZero() optimises for iterating over non zero
elements hence result is still -INF getNumNonDefaultElements() == size hence it
returns -INF instead of zero. I guess i will have to go with a bool
hasNoElements/checkedNoElements based solution
{quote}
Actually, if size() == 0, I am happy with the result being ill-defined.
Probably the best course would be to simply throw an IllegalArgumentException
or something similar to signal that asking for the max of a zero sized vector
doesn't make a lot of sense.
> Solve performance issues with Vector Implementations
> ----------------------------------------------------
>
> Key: MAHOUT-300
> URL: https://issues.apache.org/jira/browse/MAHOUT-300
> Project: Mahout
> Issue Type: Improvement
> Affects Versions: 0.3
> Reporter: Robin Anil
> Fix For: 0.3
>
> Attachments: MAHOUT-300.patch, MAHOUT-300.patch
>
>
> AbstractVector operations like times
> public Vector times(double x) {
> Vector result = clone();
> Iterator<Element> iter = iterateNonZero();
> while (iter.hasNext()) {
> Element element = iter.next();
> int index = element.index();
> result.setQuick(index, element.get() * x);
> }
> return result;
> }
> should be implemented as follows
> public Vector times(double x) {
> Vector result = clone();
> Iterator<Element> iter = result.iterateNonZero();
> while (iter.hasNext()) {
> Element element = iter.next();
> element.set(element.get() * x);
> }
> return result;
> }
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