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A Java's Collaborative Filtering library to carry out experiments in research of Collaborative Filtering based Recommender Systems. The library has been designed from researchers to researchers.

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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.commons.math3.stat.ranking;

/**
 * Strategies for handling NaN values in rank transformations.
 * 
 * MINIMAL - NaNs are treated as minimal in the ordering, equivalent to
 * (that is, tied with) Double.NEGATIVE_INFINITY.
 * MAXIMAL - NaNs are treated as maximal in the ordering, equivalent to
 * Double.POSITIVE_INFINITY
 * REMOVED - NaNs are removed before the rank transform is applied
 * FIXED - NaNs are left "in place," that is the rank transformation is
 * applied to the other elements in the input array, but the NaN elements
 * are returned unchanged.
 * FAILED - If any NaN is encountered in the input array, an appropriate
 * exception is thrown
 * 
 *
 * @since 2.0
 */
public enum NaNStrategy {

    /** NaNs are considered minimal in the ordering */
    MINIMAL,

    /** NaNs are considered maximal in the ordering */
    MAXIMAL,

    /** NaNs are removed before computing ranks */
    REMOVED,

    /** NaNs are left in place */
    FIXED,

    /** NaNs result in an exception
     * @since 3.1
     */
    FAILED
}