org.apache.mahout.df.data.DataUtils.java Source code

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Here is the source code for org.apache.mahout.df.data.DataUtils.java

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/**
 * 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.mahout.df.data;

import com.google.common.base.Preconditions;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

/**
 * Helper methods that deals with data lists and arrays of values
 */
public final class DataUtils {
    private DataUtils() {
    }

    /**
     * Computes the sum of the values
     * 
     * @param values
     */
    public static int sum(int[] values) {
        int sum = 0;
        for (int value : values) {
            sum += value;
        }

        return sum;
    }

    /**
     * foreach i : array1[i] += array2[i]
     */
    public static void add(int[] array1, int[] array2) {
        Preconditions.checkArgument(array1.length == array2.length, "array1.length != array2.length");
        for (int index = 0; index < array1.length; index++) {
            array1[index] += array2[index];
        }
    }

    /**
     * foreach i : array1[i] -= array2[i]
     */
    public static void dec(int[] array1, int[] array2) {
        Preconditions.checkArgument(array1.length == array2.length, "array1.length != array2.length");
        for (int index = 0; index < array1.length; index++) {
            array1[index] -= array2[index];
        }
    }

    /**
     * return the index of the maximum of the array, breaking ties randomly
     * 
     * @param rng
     *          used to break ties
     * @return index of the maximum
     */
    public static int maxindex(Random rng, int[] values) {
        int max = 0;
        List<Integer> maxindices = new ArrayList<Integer>();

        for (int index = 0; index < values.length; index++) {
            if (values[index] > max) {
                max = values[index];
                maxindices.clear();
                maxindices.add(index);
            } else if (values[index] == max) {
                maxindices.add(index);
            }
        }

        return maxindices.size() > 1 ? maxindices.get(rng.nextInt(maxindices.size())) : maxindices.get(0);
    }
}