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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
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*
* 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
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// @formatter:on

package org.tensorics.core.tensor.operations;

import java.util.Collection;
import java.util.HashSet;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

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;

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableMultimap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Multimap;

/**
 * Provides methods to describe how to produce a map out of a tensor.
 * 
 * This is part of a tensoric-internal fluent API
 * 
 * @author kfuchsbe
 * @param  the type of values of the tensor
 */
public final class OngoingMapOut {
    private final Tensor tensor;

    public OngoingMapOut(Tensor tensor) {
        this.tensor = tensor;
    }

    public  Tensor> inDirectionOf(Class dimension) {
        Builder> tensorBuilder = ImmutableTensor
                .builder(OngoingMapOut.dimensionsExcept(tensor.shape().dimensionSet(), dimension));

        tensorBuilder.setTensorContext(tensor.context());

        Multimap, Entry> fullEntries = groupBy(tensor.asMap().entrySet(), dimension);
        for (Set key : fullEntries.keySet()) {
            Map values = mapByDimension(fullEntries.get(key), dimension);
            tensorBuilder.at(Position.of(key)).put(values);
        }
        return tensorBuilder.build();
    }

    private static  Set coordinatesExcept(Collection coordinates, Class dimension) {
        ImmutableSet.Builder