Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/539#discussion_r27321365
--- Diff:
flink-staging/flink-ml/src/main/scala/org/apache/flink/ml/math/SparseMatrix.scala
---
@@ -0,0 +1,235 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.ml.math
+
+import scala.util.Sorting
+
+/** Sparse matrix using the compressed sparse column (CSC) representation.
+ *
+ * More details concerning the compressed sparse column (CSC)
representation can be found
+ *
[http://en.wikipedia.org/wiki/Sparse_matrix#Compressed_sparse_column_.28CSC_or_CCS.29].
+ *
+ * @param numRows Number of rows
+ * @param numCols Number of columns
+ * @param rowIndices Array containing the row indices of non-zero entries
+ * @param colPtrs Array containing the starting offsets in data for each
column
+ * @param data Array containing the non-zero entries in column-major order
+ */
+class SparseMatrix(
+ val numRows: Int,
+ val numCols: Int,
+ val rowIndices: Array[Int],
+ val colPtrs: Array[Int],
+ val data: Array[Double])
+ extends Matrix {
+
+ /** Element wise access function
+ *
+ * @param row row index
+ * @param col column index
+ * @return matrix entry at (row, col)
+ */
+ override def apply(row: Int, col: Int): Double = {
+
+ val index = locate(row, col)
+
+ if(index < 0){
+ 0
+ } else {
+ data(index)
+ }
+ }
+
+ def toDenseMatrix: DenseMatrix = {
+ val result = DenseMatrix.zeros(numRows, numCols)
+
+ for(row <- 0 until numRows; col <- 0 until numCols) {
+ result(row, col) = apply(row, col)
+ }
+
+ result
+ }
+
+ /** Element wise update function
+ *
+ * @param row row index
+ * @param col column index
+ * @param value value to set at (row, col)
+ */
+ override def update(row: Int, col: Int, value: Double): Unit = {
+ val index = locate(row, col)
+
+ if(index < 0) {
+ throw new IllegalArgumentException("Cannot update zero value of
sparse matrix at index " +
+ s"($row, $col)")
+ } else {
+ data(index) = value
+ }
+ }
+
+ override def toString: String = {
+ val result = StringBuilder.newBuilder
+
+ result.append(s"SparseMatrix($numRows, $numCols)\n")
+
+ var columnIndex = 0
+
+ val fieldWidth = math.max(numRows, numCols).toString.length
+ val valueFieldWidth = data.map(_.toString.length).max + 2
+
+ for(index <- 0 until colPtrs.last) {
+ while(colPtrs(columnIndex + 1) <= index){
+ columnIndex += 1
+ }
+
+ val rowStr = rowIndices(index).toString
+ val columnStr = columnIndex.toString
+ val valueStr = data(index).toString
+
+ result.append("(" + " " * (fieldWidth - rowStr.length) + rowStr +
"," +
+ " " * (fieldWidth - columnStr.length) + columnStr + ")")
+ result.append(" " * (valueFieldWidth - valueStr.length) + valueStr)
+ result.append("\n")
+ }
+
+ result.toString
+ }
+
+ private def locate(row: Int, col: Int): Int = {
+ require(0 <= row && row < numRows, s"Row $row is out of bounds [0,
$numRows).")
+ require(0 <= col && col < numCols, s"Col $col is out of bounds [0,
$numCols).")
--- End diff --
Well but actually the string interpolations do not costs anything, because
the message parameter is called by-name. Meaning that it is only evaluated in
case of a false requirement.
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