| /* |
| * 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.sysds.runtime.compress.estim.sample; |
| |
| import org.apache.sysds.runtime.compress.utils.Bitmap; |
| |
| public class ShlosserEstimator { |
| |
| /** |
| * Peter J. Haas, Jeffrey F. Naughton, S. Seshadri, and Lynne Stokes. Sampling-Based Estimation of the Number of |
| * Distinct Values of an Attribute. VLDB'95, Section 3.2. |
| * |
| * @param ubm The Uncompressed Bitmap containing the data from the sample |
| * @param nRows The original number of rows in the entire input |
| * @param sampleSize The number of rows in the sample |
| * @return an estimation of number of distinct values. |
| */ |
| public static int get(Bitmap ubm, int nRows, int sampleSize) { |
| double q = ((double) sampleSize) / nRows; |
| double oneMinusQ = 1 - q; |
| |
| int numVals = ubm.getNumValues(); |
| int[] freqCounts = FrequencyCount.get(ubm); |
| |
| double numerSum = 0, denomSum = 0; |
| int iPlusOne = 1; |
| for(int i = 0; i < freqCounts.length; i++, iPlusOne++) { |
| numerSum += Math.pow(oneMinusQ, iPlusOne) * freqCounts[i]; |
| denomSum += iPlusOne * q * Math.pow(oneMinusQ, i) * freqCounts[i]; |
| } |
| int estimate = (int) Math.round(numVals + freqCounts[0] * numerSum / denomSum); |
| return estimate < 1 ? 1 : estimate; |
| } |
| } |