[jira] [Commented] (MAHOUT-790) Redundancy in Matrix API, view or get?

["Lance Norskog (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13088293#comment-13088293 ] 

Lance Norskog commented on MAHOUT-790:
--------------------------------------

Cardinality array: definitely- it is mutable from outside. 
    final int row; 
    final int column;

viewColumn v.s. getColumn: the question here is deep v.s. shallow copy?
I would go with
    getColumn(int column) and getColumn(int column, Vector v)
where getColumn(int column) is assumed to give a shallow copy.

Diagonals: are they really needed now? Should there be triangular or symmetric?

getNumNondefault: this requires being able to produce the number, which is a "design load". It is not used much in "real code". I suspect most of those users could track/deduce the number in some other way, rather than expect the object to remember it.

> Redundancy in Matrix API, view or get?
> --------------------------------------
>
>                 Key: MAHOUT-790
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-790
>             Project: Mahout
>          Issue Type: Improvement
>            Reporter: Ted Dunning
>
> We have a bunch of redundant methods in our matrix interface.  These include things that return views of parts of the matrix:
> {code}
>   Matrix viewPart(int[] offset, int[] size);
>   Matrix viewPart(int rowOffset, int rowsRequested, int columnOffset, int columnsRequested);
>   Vector viewRow(int row);
>   Vector viewColumn(int column);
> {code}
> and things that do the same but call refer to getting stuff
> {code}
>   Vector getColumn(int column);
>   Vector getRow(int row);
>   double getQuick(int row, int column);
>   int[] getNumNondefaultElements();
>   Map<String, Integer> getColumnLabelBindings();
>   Map<String, Integer> getRowLabelBindings();
>   double get(String rowLabel, String columnLabel);
> {code}
> To my mind, get implies a get-by-value whereas view implies get-by-reference.  As such, I would suggest that getColumn and getRow should disappear.  On the other hand, getQuick and get are both correctly named.  
> This raises the question of what getNumNondefaultElements really does.  I certainly can't tell just from the signature.  Is it too confusing to keep?
> Additionally, what do people think that getColumnLabelBindings and getRowLabelBindings return?  A mutable map?  Or an immutable one?
> Under the covers, viewRow and viewColumn (and the upcoming viewDiagonal) have default implementations that use MatrixVectorView, but AbstractMatrix doesn't have an implementation for getRow and getColumn. 
> In sum, I suggest that:
>   - getRow and getColumn go away
>   - the fancy fast implementations fo getRow and getColumn that exist be migrated to be over-rides of viewRow and viewColumn
>   - there be a constructor for AbstractMatrix that sets the internal size things correctly.
>   - that the internal cardinality array in AbstractMatrix goes away to be replaced by two integers.
>   - viewDiagonal() and viewDiagonal(length) and viewDiagonal(row, column) and viewDiagonal(int row, column, length) be added.
> I will produce a patch shortly.

--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira