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Tensorics is a java framework which uses a tensor as a central object. A tensor represents a set of values placed in an N-dimensional space. Wherever you are tempted to use maps of maps, a tensor might be a good choice ;-) Tensorics provides methods to create, transform and performing calculations with those tensors.

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// @formatter:off
 /*******************************************************************************
 *
 * This file is part of tensorics.
 * 
 * Copyright (c) 2008-2011, CERN. All rights reserved.
 *
 * Licensed 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.
 * 
 ******************************************************************************/
// @formatter:on

package org.tensorics.incubate.function;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.SortedMap;

import com.google.common.collect.ImmutableSortedMap;

/**
 * This implementation of {@link KeyValueFunction} only provides values at discrete points of X argument. If value is
 * requested for unavailable value an {@link IllegalDiscreteFunctionUsageException} is thrown.
 * 
 * @author agorzaws
 * @param  function arguments type
 * @param  function values type
 */
public class SortedMapBackedDiscreteFunction, Y> implements DiscreteFunction,
        Serializable {
    private static final long serialVersionUID = 1L;

    private final SortedMap function;
    private final SortedMap errors;
    private final InterpolationStrategy interpolationStrategy;
    private final String name;

    // private Tensor functionTensor;
    /**
     * @param builder
     */
    SortedMapBackedDiscreteFunction(Builder builder) {
        super();
        this.function = builder.mapBuilder.build();
        this.errors = builder.errorsBuilder.build();
        this.interpolationStrategy = builder.interpolationStrategy;
        this.name = builder.name;
    }

    @Override
    public Y getY(X xValue) {
        Y value = function.get(xValue);
        if (value != null) {
            return value;
        }
        if (interpolationStrategy == null) {
            throw new IllegalDiscreteFunctionUsageException(
                    "No interpolation Strategy found and No values can be found for given argument: " + xValue);
        }
        return interpolationStrategy.interpolate(xValue, this);
    }

    @Override
    public List getXs() {
        return new ArrayList<>(function.keySet());
    }

    @Override
    public List getYs() {
        return new ArrayList<>(function.values());
    }

    @Override
    public List getYsErr() {
        return new ArrayList<>(errors.values());
    }

    @Override
    public String getName() {
        return name;
    }

    /**
     * The builder for the function based on a sorted map. This class provides methods to add values to the function.
     * 
     * @author kfuchsbe
     * @param  the type of the values in x-direction (Independent variable)
     * @param  the type of the values in y-direction (Dependent variable)
     */
    public static final class Builder, Y> implements DiscreteFunctionBuilder {

        private static final String NO_NAME = "NO NAME";

        private String name = NO_NAME;
        private final ImmutableSortedMap.Builder mapBuilder = ImmutableSortedMap.naturalOrder();
        private final ImmutableSortedMap.Builder errorsBuilder = ImmutableSortedMap.naturalOrder();

        private InterpolationStrategy interpolationStrategy = null;

        Builder() {
            /* Should only be instantiated from the static method */
        }

        public DiscreteFunctionBuilder put(Entry entry) {
            mapBuilder.put(entry);
            return this;
        }

        @Override
        public DiscreteFunctionBuilder put(X key, Y value) {
            mapBuilder.put(key, value);
            return this;
        }

        @Override
        public DiscreteFunctionBuilder put(X key, Y value, Y error) {
            mapBuilder.put(key, value);
            errorsBuilder.put(key, error);
            return this;
        }

        public DiscreteFunctionBuilder putAll(Map values) {
            mapBuilder.putAll(values);
            return this;
        }

        @Override
        public DiscreteFunctionBuilder withInterpolationStrategy(InterpolationStrategy strategy) {
            this.interpolationStrategy = strategy;
            return this;
        }

        @Override
        public DiscreteFunctionBuilder withName(String newName) {
            this.name = newName;
            return this;
        }

        @Override
        public SortedMapBackedDiscreteFunction build() {
            return new SortedMapBackedDiscreteFunction<>(this);
        }
    }

    public static final , Y> Builder builder() {
        return new Builder<>();
    }

}