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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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 * This file is part of tensorics.
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 * 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
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// @formatter:on

package org.tensorics.core.tensor.operations;

import java.util.Map;
import java.util.Map.Entry;

import org.tensorics.core.commons.operations.Conversion;
import org.tensorics.core.reduction.ReductionStrategy;
import org.tensorics.core.tensor.Context;
import org.tensorics.core.tensor.ImmutableTensor;
import org.tensorics.core.tensor.ImmutableTensor.Builder;
import org.tensorics.core.tensor.Position;
import org.tensorics.core.tensor.Tensor;

/**
 * The operation which describes the reduction of a tensor in one direction.
 * 
 * @author kfuchsbe
 * @param  the dimension (direction, type of coordinate) in which the tensor will be reduced
 * @param  the type of the elements of the tensor
 */
public class TensorReduction implements Conversion, Tensor> {

    private final Class direction;
    private final ReductionStrategy reductionStrategy;

    public TensorReduction(Class direction, ReductionStrategy strategy) {
        super();
        this.direction = direction;
        this.reductionStrategy = strategy;
    }

    @Override
    public Tensor apply(Tensor value) {
        Tensor> mapped = TensorInternals.mapOut(value).inDirectionOf(direction);

        Builder builder = ImmutableTensor.builder(mapped.shape().dimensionSet());
        builder.setTensorContext(Context.of(reductionStrategy.context(value.context().getPosition()).coordinates()));
        for (Entry> entry : mapped.asMap().entrySet()) {
            R reducedValue = reductionStrategy.reduce(entry.getValue(), entry.getKey());
            if (reducedValue != null) {
                builder.at(entry.getKey()).put(reducedValue);
            }
        }
        return builder.build();
    }

}