Github user sethah commented on a diff in the pull request:
https://github.com/apache/spark/pull/15628#discussion_r105806817
--- Diff:
mllib-local/src/main/scala/org/apache/spark/ml/linalg/Matrices.scala ---
@@ -153,6 +154,97 @@ sealed trait Matrix extends Serializable {
*/
@Since("2.0.0")
def numActives: Int
+
+ /**
+ * Converts this matrix to a sparse matrix.
+ *
+ * @param colMajor Whether the values of the resulting sparse matrix
should be in column major
+ * or row major order. If `false`, resulting matrix
will be row major.
+ */
+ private[ml] def toSparseMatrix(colMajor: Boolean): SparseMatrix
+
+ /**
+ * Converts this matrix to a sparse matrix in column major order.
+ */
+ @Since("2.2.0")
+ def toCSCMatrix: SparseMatrix = toSparseMatrix(colMajor = true)
+
+ /**
+ * Converts this matrix to a sparse matrix in row major order.
+ */
+ @Since("2.2.0")
+ def toCSRMatrix: SparseMatrix = toSparseMatrix(colMajor = false)
+
+ /**
+ * Converts this matrix to a sparse matrix in column major order.
+ */
+ @Since("2.2.0")
+ def toSparse: SparseMatrix = toSparseMatrix(colMajor = true)
+
+ /**
+ * Converts this matrix to a dense matrix.
+ *
+ * @param colMajor Whether the values of the resulting dense matrix
should be in column major
+ * or row major order. If `false`, resulting matrix
will be row major.
+ */
+ private[ml] def toDenseMatrix(colMajor: Boolean): DenseMatrix
+
+ /**
+ * Converts this matrix to a dense matrix in column major order.
+ */
+ @Since("2.2.0")
+ def toDense: DenseMatrix = toDenseMatrix(colMajor = true)
+
+ /**
+ * Returns a matrix in either dense or sparse format, whichever uses
less storage.
+ *
+ * @param colMajor Whether the values of the resulting matrix should be
in column major
+ * or row major order. If `false`, resulting matrix
will be row major.
+ */
+ @Since("2.2.0")
+ def compressed(colMajor: Boolean): Matrix = {
+ if (getDenseSizeInBytes < getSparseSizeInBytes(colMajor)) {
+ toDenseMatrix(colMajor)
+ } else {
+ toSparseMatrix(colMajor)
+ }
+ }
+
+ /**
+ * Returns a matrix in dense column major, dense row major, sparse row
major, or sparse column
+ * major format, whichever uses less storage. When dense representation
is optimal, it maintains
+ * the current layout order.
+ */
+ @Since("2.2.0")
+ def compressed: Matrix = {
--- End diff --
It's only a problem if we override/implement it in a subclass. Since it's
contained wholly in the trait, it will be fine. I think this is ok to leave,
though we could make it final? Also we could make three methods: `compressed`,
`compressedCSC`, `compressedCSR`. I think the latter is a good solution,
thoughts?
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