[
https://issues.apache.org/jira/browse/MAHOUT-790?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13090377#comment-13090377
]
Ted Dunning commented on MAHOUT-790:
------------------------------------
{quote}
But it does show that perhaps viewPart should be done outside of Matrix.
{quote}
I think not. Getting a view of a submatrix or row or column or diagonal is a
fundamental operation in linear algebra. The method may delegate to a view
class, but to the user, it should appear as a matrix operation.
Besides, there are are kinds of matrices and vectors where the view *is* the
same type as the matrix. For instance, for dense matrices this is often true
because the dense matrix is a one-dimensional storage array combined with an
offset plus row and column strides. Any block-wise view of this keeps the same
storage and has different offset and strides.
On the other hand, sparse matrices do better with a view structure.
In any caes, viewPart should be a method on the matrix. It should return a
matrix and preserve sparsity and maybe a few related properties, but not
precise type.
> Redundancy in Matrix API, view or get?
> --------------------------------------
>
> Key: MAHOUT-790
> URL: https://issues.apache.org/jira/browse/MAHOUT-790
> Project: Mahout
> Issue Type: Improvement
> Affects Versions: 0.5
> Reporter: Ted Dunning
> Fix For: 0.6
>
> Attachments: MAHOUT-790.patch
>
>
> 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
