MDHistoWorkspaceIterator.cpp

// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2018 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
#include "MantidDataObjects/MDHistoWorkspaceIterator.h"
#include "MantidGeometry/MDGeometry/IMDDimension.h"
#include "MantidKernel/System.h"
#include "MantidKernel/Utils.h"
#include "MantidKernel/VMD.h"
#include <algorithm>
#include <boost/math/special_functions/round.hpp>
#include <functional>
#include <numeric>
#include <utility>

using namespace Mantid::Kernel;
using namespace Mantid::API;
using Mantid::Geometry::IMDDimension_const_sptr;

namespace {
// To get the rounded difference, we need to take into account precision issues
// which arise when
// the bin centres match
Mantid::coord_t getDExact(Mantid::coord_t location, Mantid::coord_t origin, Mantid::coord_t binWidth) {
  auto dExact = (location - origin) / binWidth;
  const auto tolerance = Mantid::coord_t(1e-5);

  // Expl. of the steps below
  // -1     -0.5       0      0.5        1   where integer values are bin
  // boundaries and half-values
  //  |       |        |       |         |   are bin centres
  //                               |
  //                              Location
  // Goal: Find distance to closest bin centre:
  // 1. Get the predecimal value of the location: here 0
  // 2. Add and subtract 0.5 to find two possible centres: here -0.5 adn + 0.5
  // 3. Find the centre which minimizes the difference to the location
  // 4. Keep the difference (distance) that was calculation in the step above

  // Get the two centre indices which are the closest to dExact.
  const auto centre1 = static_cast<Mantid::coord_t>(size_t(dExact)) + 0.5;
  const auto centre2 = static_cast<Mantid::coord_t>(size_t(dExact)) - 0.5;

  // Calculate the distance of the location to the centres
  const auto diff1 = static_cast<Mantid::coord_t>(fabs(centre1 - dExact));
  const auto diff2 = static_cast<Mantid::coord_t>(fabs(centre2 - dExact));

  const auto difference = diff1 < diff2 ? diff1 : diff2;

  // If the differnce is within the tolerance, ie the location is essentially on
  // the centre, then
  // we want to be on the left of that centre. The correct index for when we are
  // on the centre,
  // is the lower next integer value.
  if (difference < tolerance) {
    if (difference == 0.0f) {
      dExact -= tolerance; // When we have an exact hit in the centre, give it a
                           // nudge to the lower bin boundary
    } else {
      dExact -= 2 * difference; // Need to subtract twice the differnce, in
                                // order to be guaranteed below the centre
    }
  }
  return dExact;
}
} // namespace

namespace Mantid::DataObjects {

//----------------------------------------------------------------------------------------------
/** Constructor
 *
 * @param workspace :: MDHistoWorkspace_sptr being iterated
 * @param function :: The implicit function to use. Becomes owned by this
 *object.
 * @return
 */

//----------------------------------------------------------------------------------------------
/**
 * Constructor
 * @param workspace :: MDHistoWorkspace_sptr being iterated
 * @param function :: The implicit function to use. Becomes owned by this
 * object.
 * @param beginPos :: start position
 * @param endPos :: end position
 */
MDHistoWorkspaceIterator::MDHistoWorkspaceIterator(const MDHistoWorkspace_const_sptr &workspace,
                                                   Mantid::Geometry::MDImplicitFunction *function, size_t beginPos,
                                                   size_t endPos)
    : m_skippingPolicy(new SkipMaskedBins(this)) {
  this->init(workspace.get(), function, beginPos, endPos);
}

/**
 * Constructor
 * @param workspace :: MDHistoWorkspace_sptr being iterated
 * @param function :: The implicit function to use. Becomes owned by this
 * object.
 * @param beginPos
 * @param endPos
 */
MDHistoWorkspaceIterator::MDHistoWorkspaceIterator(const MDHistoWorkspace *workspace,
                                                   Mantid::Geometry::MDImplicitFunction *function, size_t beginPos,
                                                   size_t endPos)
    : m_skippingPolicy(new SkipMaskedBins(this)) {
  this->init(workspace, function, beginPos, endPos);
}

/**
 * Constructor
 * @param workspace :: MDHistoWorkspace_sptr being iterated
 * @param skippingPolicy :: The skipping policy to use.
 * @param function :: The implicit function to use. Becomes owned by this
 * object.
 * @param beginPos :: Start position
 * @param endPos :: End position
 */
MDHistoWorkspaceIterator::MDHistoWorkspaceIterator(const MDHistoWorkspace_const_sptr &workspace,
                                                   SkippingPolicy *skippingPolicy,
                                                   Mantid::Geometry::MDImplicitFunction *function, size_t beginPos,
                                                   size_t endPos)
    : m_skippingPolicy(skippingPolicy) {
  this->init(workspace.get(), function, beginPos, endPos);
}

//----------------------------------------------------------------------------------------------
/** Constructor
 *
 * @param workspace :: MDHistoWorkspace_sptr being iterated
 * @param function :: The implicit function to use. Becomes owned by this
 *object.
 * @param skippingPolicy :: The skipping policy to use
 * @param beginPos :: Start position
 * @param endPos :: End position
 * @return
 */
MDHistoWorkspaceIterator::MDHistoWorkspaceIterator(const MDHistoWorkspace *workspace, SkippingPolicy *skippingPolicy,
                                                   Mantid::Geometry::MDImplicitFunction *function, size_t beginPos,
                                                   size_t endPos)
    : m_skippingPolicy(skippingPolicy) {
  this->init(workspace, function, beginPos, endPos);
}

/**
 * Constructor helper
 * @param workspace :: MDWorkspace
 * @param function :: implicit function or NULL for none. Gains ownership of the
 * pointer.
 * @param beginPos :: Start position
 * @param endPos :: End position
 */
void MDHistoWorkspaceIterator::init(const MDHistoWorkspace *workspace, Mantid::Geometry::MDImplicitFunction *function,
                                    size_t beginPos, size_t endPos) {
  m_ws = workspace;
  if (m_ws == nullptr)
    throw std::invalid_argument("MDHistoWorkspaceIterator::ctor(): NULL workspace given.");

  m_begin = beginPos;
  m_pos = m_begin;
  m_function.reset(function);

  m_max = endPos;
  if (m_max > m_ws->getNPoints())
    m_max = m_ws->getNPoints();
  if (m_max < m_pos)
    throw std::invalid_argument("MDHistoWorkspaceIterator::ctor(): End point "
                                "given is before the start point.");

  m_nd = m_ws->getNumDims();
  m_center = new coord_t[m_nd];
  m_origin = new coord_t[m_nd];
  m_binWidth = new coord_t[m_nd];
  m_index = new size_t[m_nd];
  m_indexMax = new size_t[m_nd];
  m_indexMaker = new size_t[m_nd];
  Utils::NestedForLoop::SetUp(m_nd, m_index, 0);
  // Initalize all these values
  for (size_t d = 0; d < m_nd; d++) {
    IMDDimension_const_sptr dim = m_ws->getDimension(d);
    m_center[d] = 0;
    m_origin[d] = dim->getMinimum();
    m_binWidth[d] = dim->getBinWidth();
    m_indexMax[d] = dim->getNBins();
  }
  Utils::NestedForLoop::SetUpIndexMaker(m_nd, m_indexMaker, m_indexMax);

  // Initialize the current index from the start position.
  Utils::NestedForLoop::GetIndicesFromLinearIndex(m_nd, m_pos, m_indexMaker, m_indexMax, m_index);

  // Make sure that the first iteration is at a point inside the implicit
  // function
  if (m_function) {
    // Calculate the center of the 0-th bin
    for (size_t d = 0; d < m_nd; d++)
      m_center[d] = m_origin[d] + 0.5f * m_binWidth[d];
    // Skip on if the first point is NOT contained
    if (!m_function->isPointContained(m_center)) {
      bool didNext = next();
      if (!didNext && this->valid()) {
        throw std::runtime_error("Inconsistency found initializing "
                                 "MDHistoWorkspace iterator: this iterator should be valid, but "
                                 "when tried to skip the "
                                 "first point (not contained) could not iterate to "
                                 "next point.");
      }
    }
  }

  // --- Calculate index permutations for neighbour finding face touching ---
  auto temp = std::vector<int64_t>(2 * m_nd);
  m_permutationsFaceTouching.swap(temp);

  int64_t offset = 1;

  m_permutationsFaceTouching[0] = -1;
  m_permutationsFaceTouching[1] = 1;

  // Figure out what possible indexes deltas to generate indexes that are next
  // to the current one.
  for (size_t j = 1; j < m_nd; ++j) {
    offset = offset * static_cast<int64_t>(m_ws->getDimension(j - 1)->getNBins());

    m_permutationsFaceTouching[j * 2] = offset;
    m_permutationsFaceTouching[(j * 2) + 1] = -offset;
  }
}

//----------------------------------------------------------------------------------------------
/** Destructor
 */
MDHistoWorkspaceIterator::~MDHistoWorkspaceIterator() {
  delete[] m_center;
  delete[] m_origin;
  delete[] m_binWidth;
  delete[] m_index;
  delete[] m_indexMax;
  delete[] m_indexMaker;
}
//----------------------------------------------------------------------------------------------
/** @return the number of points to be iterated on */
size_t MDHistoWorkspaceIterator::getDataSize() const { return size_t(m_max - m_begin); }

//----------------------------------------------------------------------------------------------
/** Jump to the index^th cell.
 *  No range checking is performed, for performance reasons!
 *
 * @param index :: point to jump to. Must be 0 <= index < getDataSize().
 */
void MDHistoWorkspaceIterator::jumpTo(size_t index) { m_pos = uint64_t(index + m_begin); }

/**
 * Jump the iterator to the nearest valid position correspoinding to the centre
 * current position of the desired iterator position.
 * @param fromLocation : destination or nearest to.
 * @return absolute distance of end position from requested position.
 */
Mantid::coord_t MDHistoWorkspaceIterator::jumpToNearest(const VMD &fromLocation) {
  std::vector<size_t> indexes(m_nd);
  coord_t sqDiff = 0;
  for (size_t d = 0; d < m_nd; ++d) {
    coord_t dExact = getDExact(fromLocation[d], m_origin[d], m_binWidth[d]);
    size_t dRound = std::lround(dExact); // Round to nearest bin edge.
    if (dRound >= m_indexMax[d]) {
      dRound = m_indexMax[d] - 1;
    }
    sqDiff += (dExact - coord_t(dRound)) * (dExact - coord_t(dRound)) * m_binWidth[d] * m_binWidth[d];
    indexes[d] = dRound;
  }

  const size_t linearIndex = Utils::NestedForLoop::GetLinearIndex(m_nd, &indexes[0], m_indexMaker);
  this->jumpTo(linearIndex);
  return std::sqrt(sqDiff);
}

//----------------------------------------------------------------------------------------------
/** @return true if the iterator is valid. Check this at the start of an
 * iteration,
 * in case the very first point is not valid.
 */
bool MDHistoWorkspaceIterator::valid() const { return (m_pos < m_max); }

//----------------------------------------------------------------------------------------------
/// Advance to the next cell. If the current cell is the last one in the
/// workspace
/// do nothing and return false.
/// @return true if you can continue iterating
bool MDHistoWorkspaceIterator::next() {
  if (m_function) {
    bool allIncremented;

    do {
      m_pos++;
      allIncremented = Utils::NestedForLoop::Increment(m_nd, m_index, m_indexMax);
      // Calculate the center
      for (size_t d = 0; d < m_nd; d++) {
        m_center[d] = m_origin[d] + (coord_t(m_index[d]) + 0.5f) * m_binWidth[d];
      }
      // Keep incrementing until you are in the implicit function and not masked
    } while (m_pos < m_max &&
             ((!allIncremented && !m_function->isPointContained(m_center)) || m_skippingPolicy->keepGoing()));
  } else {
    // Keep moving to next position if the current position is masked and
    // still valid.
    do {
      m_pos++;
    } while (m_pos < m_max && m_skippingPolicy->keepGoing());
  }

  bool ret = m_pos < m_max;
  // Go through every point;
  return ret;
}

//----------------------------------------------------------------------------------------------
/// Advance, skipping a certain number of cells.
/// @param skip :: how many to increase. If 1, then every point will be sampled.
bool MDHistoWorkspaceIterator::next(size_t skip) {
  m_pos += skip;

  return (m_pos < m_max);
}

//----------------------------------------------------------------------------------------------
/// Returns the normalized signal for this box
signal_t MDHistoWorkspaceIterator::getNormalizedSignal() const {
  // What is our normalization factor?
  switch (m_normalization) {
  case NoNormalization:
    return m_ws->getSignalAt(m_pos);
  case VolumeNormalization:
    return m_ws->getSignalAt(m_pos) * m_ws->getInverseVolume();
  case NumEventsNormalization:
    return m_ws->getSignalAt(m_pos) / m_ws->getNumEventsAt(m_pos);
  }
  // Should not reach here
  return std::numeric_limits<signal_t>::quiet_NaN();
}

//----------------------------------------------------------------------------------------------
/// Returns the normalized error for this box
signal_t MDHistoWorkspaceIterator::getNormalizedError() const {
  // What is our normalization factor?
  switch (m_normalization) {
  case NoNormalization:
    return m_ws->getErrorAt(m_pos);
  case VolumeNormalization:
    return m_ws->getErrorAt(m_pos) * m_ws->getInverseVolume();
  case NumEventsNormalization:
    return m_ws->getErrorAt(m_pos) / m_ws->getNumEventsAt(m_pos);
  }
  // Should not reach here
  return std::numeric_limits<signal_t>::quiet_NaN();
}

//----------------------------------------------------------------------------------------------
/// Returns the signal for this box, same as innerSignal
signal_t MDHistoWorkspaceIterator::getSignal() const { return m_ws->getSignalAt(m_pos); }

/// Returns the error for this box, same as innerError
signal_t MDHistoWorkspaceIterator::getError() const { return m_ws->getErrorAt(m_pos); }
//----------------------------------------------------------------------------------------------
/// Return a list of vertexes defining the volume pointed to
std::unique_ptr<coord_t[]> MDHistoWorkspaceIterator::getVertexesArray(size_t &numVertices) const {
  // The MDHistoWorkspace takes care of this
  return m_ws->getVertexesArray(m_pos, numVertices);
}

std::unique_ptr<coord_t[]> MDHistoWorkspaceIterator::getVertexesArray(size_t &numVertices, const size_t outDimensions,
                                                                      const bool *maskDim) const {
  // Do the same thing as is done in the MDBoxBase
  UNUSED_ARG(numVertices);
  UNUSED_ARG(outDimensions);
  UNUSED_ARG(maskDim);
  throw std::runtime_error("Not Implemented At present time");
}

//----------------------------------------------------------------------------------------------
/// Returns the position of the center of the box pointed to.
Mantid::Kernel::VMD MDHistoWorkspaceIterator::getCenter() const {
  // Get the indices
  Utils::NestedForLoop::GetIndicesFromLinearIndex(m_nd, m_pos, m_indexMaker, m_indexMax, m_index);
  // Find the center
  for (size_t d = 0; d < m_nd; ++d) {
    m_center[d] = m_origin[d] + (coord_t(m_index[d]) + 0.5f) * m_binWidth[d];
  }
  return VMD(m_nd, m_center);
}

/**
 * Get the extents in n-dimensions corresponding to the position of the box of
 * the current iterator.
 * @return pairs of min/max extents.
 */
VecMDExtents MDHistoWorkspaceIterator::getBoxExtents() const {

  // Get the indexes.
  Utils::NestedForLoop::GetIndicesFromLinearIndex(m_nd, m_pos, m_indexMaker, m_indexMax, m_index);
  VecMDExtents extents(m_nd);
  // Find the extents.
  for (size_t d = 0; d < m_nd; ++d) {
    const coord_t min = m_origin[d] + coord_t(m_index[d]) * m_binWidth[d]; // Min in d
    const coord_t max = min + m_binWidth[d];                               // Max in d
    extents[d] = MDExtentPair(min, max);
  }

  return extents;
}

//----------------------------------------------------------------------------------------------
/// Returns the number of events/points contained in this box
/// @return truncated number of events
size_t MDHistoWorkspaceIterator::getNumEvents() const { return static_cast<size_t>(this->getNumEventsFraction()); }

//----------------------------------------------------------------------------------------------
/// Returns the number of events/points contained in this box
/// @return eact number of events (weights may be applied)
signal_t MDHistoWorkspaceIterator::getNumEventsFraction() const { return m_ws->getNumEventsAt(m_pos); }

//----------------------------------------------------------------------------------------------
/// For a given event/point in this box, return the associated experiment-info index
uint16_t MDHistoWorkspaceIterator::getInnerExpInfoIndex(size_t /*index*/) const {
  return 0;
  // throw std::runtime_error("MDHistoWorkspaceIterator: No events are
  // contained, so it is not possible to return inner associated experiment-info index.");
}

/// For a given event/point in this box, return the goniometer index
uint16_t MDHistoWorkspaceIterator::getInnerGoniometerIndex(size_t /*index*/) const {
  return 0;
  // throw std::runtime_error("MDHistoWorkspaceIterator: No events are
  // contained, so it is not possible to return inner goniometer index.");
}

/// For a given event/point in this box, return the detector ID
int32_t MDHistoWorkspaceIterator::getInnerDetectorID(size_t /*index*/) const {
  return 0;
  // throw std::runtime_error("MDHistoWorkspaceIterator: No events are
  // contained, so it is not possible to return inner detector ID.");
}

/// Returns the position of a given event for a given dimension
coord_t MDHistoWorkspaceIterator::getInnerPosition(size_t /*index*/, size_t dimension) const {
  return m_ws->getCenter(m_pos)[dimension];
}

/// Returns the signal of a given event
signal_t MDHistoWorkspaceIterator::getInnerSignal(size_t /*index*/) const { return m_ws->getSignalAt(m_pos); }

/// Returns the error of a given event
signal_t MDHistoWorkspaceIterator::getInnerError(size_t /*index*/) const { return m_ws->getErrorAt(m_pos); }

bool MDHistoWorkspaceIterator::getIsMasked() const { return m_ws->getIsMaskedAt(m_pos); }

/**
 Getter for the linear index
 @return the linear index.
 */
size_t MDHistoWorkspaceIterator::getLinearIndex() const { return m_pos; }

/**
 * Gets indexes of bins/pixels/boxes neighbouring the present iterator location.
 Return all vertex touching neighbours.
 * The number of neighbour indexes returned will depend upon the dimensionality
 of the workspace as well as the presence
 * of boundaries and edges.

 FindNeighbours will return the indexes of neighbours even if they are
 unreachable from the current iterator.
 To verify that the indexes are reachable from the current iterator, run
 isWithinBounds. Note that this is only a concern
 where the workspace iteration is portioned up amongst >1 iterators.

 * @return vector of linear indexes to neighbour locations.
 */
std::vector<size_t> MDHistoWorkspaceIterator::findNeighbourIndexes() const {

  return this->findNeighbourIndexesByWidth(3 /*immediate neighbours only*/);
}

/**
 * Find neighbor indexes, but only return those that are face-touching.
 *
 * Will return the indexes of neighbours even if they are unreachable from the
 *current iterator.
 * To verify that the indexes are reachable from the current iterator, run
 *isWithinBounds. Note that this is only a concern where the workspace iteration
 *is portioned up amongst >1 iterators.
 * @return
 */
std::vector<size_t> MDHistoWorkspaceIterator::findNeighbourIndexesFaceTouching() const {
  Utils::NestedForLoop::GetIndicesFromLinearIndex(m_nd, m_pos, m_indexMaker, m_indexMax, m_index);

  std::vector<size_t> neighbourIndexes; // Accumulate neighbour indexes.
  std::vector<int> widths(m_nd, 3);     // Face touching width is always 3 in each dimension
  for (auto permutation : m_permutationsFaceTouching) {
    if (permutation == 0) {
      continue;
    }

    size_t neighbour_index = m_pos + permutation;
    if (neighbour_index < m_ws->getNPoints() &&
        Utils::isNeighbourOfSubject(m_nd, neighbour_index, m_index, m_indexMaker, m_indexMax, widths)) {
      neighbourIndexes.emplace_back(neighbour_index);
    }
  }
  return neighbourIndexes;
}

/**
 @param index : linear index to inspect against iterator
 @return True only if the index is between the min and max bounds of the
 iterator.
 */
bool MDHistoWorkspaceIterator::isWithinBounds(size_t index) const { return index >= m_begin && index < m_max; }

/**
 * This is to create the permutations needed to operate find neighbours in the
 *vertex-touching schenarios
 * Rather than having to fabricate what the possible permutations are each time
 *the iterator is moved and the method is called,
 * we can cache the results, and re-use them as the only factors are the and the
 *dimensionality, the width (n-neighbours).
 * @param widths : vector of integer widths.
 * @return index permutations
 */
std::vector<int64_t> MDHistoWorkspaceIterator::createPermutations(const std::vector<int> &widths) const {
  // look-up
  auto it = m_permutationsVertexTouchingMap.find(widths);
  if (it == m_permutationsVertexTouchingMap.end()) {

    if (widths[0] % 2 == 0) {
      throw std::invalid_argument("MDHistoWorkspaceIterator::"
                                  "findNeighbourIndexesByWidth, width must "
                                  "always be an odd number");
    }
    if (widths.size() != m_nd) {
      throw std::invalid_argument("MDHistoWorkspaceIterator::"
                                  "findNeighbourIndexesByWidth, size of widths "
                                  "must be the same as the number of "
                                  "dimensions.");
    }

    int64_t offset = 1;

    // Size of block will be width ^ nd
    std::vector<int64_t> permutationsVertexTouching;
    // Calculate maximum permutations size.
    int product = std::accumulate(widths.begin(), widths.end(), 1, std::multiplies<int>());
    permutationsVertexTouching.reserve(product);

    int centreIndex = widths[0] / 2; // Deliberately truncate to get centre index

    for (int i = 0; i < widths[0]; ++i) {
      // for width = 3 : -1, 0, 1
      // for width = 5 : -2, -1, 0, 1, 2
      permutationsVertexTouching.emplace_back(centreIndex - i);
    }

    // Figure out what possible indexes deltas to generate indexes that are next
    // to the current one.
    for (size_t j = 1; j < m_nd; ++j) {
      offset = offset * static_cast<int64_t>(m_ws->getDimension(j - 1)->getNBins());

      size_t nEntries = permutationsVertexTouching.size();
      for (int k = 1; k <= widths[j] / 2; ++k) {
        for (size_t m = 0; m < nEntries; m++) {
          permutationsVertexTouching.emplace_back((offset * k) + permutationsVertexTouching[m]);
          permutationsVertexTouching.emplace_back((offset * k * (-1)) + permutationsVertexTouching[m]);
        }
      }
    }

    m_permutationsVertexTouchingMap.insert(std::make_pair(widths, permutationsVertexTouching));
  }

  // In either case, get the result.
  return m_permutationsVertexTouchingMap[widths];
}

/**
 * Find vertex-touching neighbours.
 *
 * Expands out the width to make a n-dimensional vector filled with the
 *requested width.
 *
 * @param width : Odd number of pixels for all dimensions.
 * @return collection of indexes.
 */
std::vector<size_t> MDHistoWorkspaceIterator::findNeighbourIndexesByWidth(const int &width) const {

  return this->findNeighbourIndexesByWidth(std::vector<int>(m_nd, width));
}

/**
 * Find vertex-touching neighbours.
 * @param widths : Vector containing odd number of pixels per dimension. Entries
 * match dimensions of iterator.
 * @return collection of indexes.
 */
std::vector<size_t> MDHistoWorkspaceIterator::findNeighbourIndexesByWidth(const std::vector<int> &widths) const {

  // Find existing or create required index permutations.
  std::vector<int64_t> permutationsVertexTouching = createPermutations(widths);

  Utils::NestedForLoop::GetIndicesFromLinearIndex(m_nd, m_pos, m_indexMaker, m_indexMax, m_index);

  // Filter out indexes that are are not actually neighbours.
  // Accumulate neighbour indexes.
  std::vector<size_t> neighbourIndexes(permutationsVertexTouching.size());
  size_t nextFree = 0;
  for (auto permutation : permutationsVertexTouching) {
    if (permutation == 0) {
      continue;
    }

    size_t neighbour_index = m_pos + permutation;
    if (neighbour_index < m_ws->getNPoints() &&
        Utils::isNeighbourOfSubject(m_nd, neighbour_index, m_index, m_indexMaker, m_indexMax, widths)) {
      neighbourIndexes[nextFree++] = neighbour_index;
    }
  }
  neighbourIndexes.resize(nextFree);

  // Remove duplicates
  std::sort(neighbourIndexes.begin(), neighbourIndexes.end());
  neighbourIndexes.erase(std::unique(neighbourIndexes.begin(), neighbourIndexes.end()), neighbourIndexes.end());
  return neighbourIndexes;
}

/**
 * Find vertex-touching neighbours. This function always returns a vector of
 * indexes which has a size equal to the product of the widths. This is
 * because it also returns a vector of bools (of the same size) which
 * records the validity of each index, rather than removing invalid indexes
 * from the list. This function only allows a width vector to have one
 * non-singleton dimension.
 * NB, the index of the central pixel is included in the output array.
 * @param width : Width in the non-singleton dimension
 * @param width_dimension : The non-singleton dimension of the widths vector
 * @return collection of indexes.
 */
std::pair<std::vector<size_t>, std::vector<bool>>
MDHistoWorkspaceIterator::findNeighbourIndexesByWidth1D(const int &width, const int &width_dimension) const {

  std::vector<int> widths;
  for (size_t dimension = 0; dimension < m_nd; ++dimension) {
    if (static_cast<int>(dimension) == width_dimension) {
      widths.emplace_back(width);
    } else {
      widths.emplace_back(1);
    }
  }

  // Find existing or create required index permutations.
  std::vector<int64_t> permutationsVertexTouching = createPermutations(widths);

  std::vector<bool> indexValidity(permutationsVertexTouching.size(), false);

  Utils::NestedForLoop::GetIndicesFromLinearIndex(m_nd, m_pos, m_indexMaker, m_indexMax, m_index);

  std::sort(permutationsVertexTouching.begin(), permutationsVertexTouching.end());

  // Accumulate neighbour indexes.
  // Record indexes as valid only if they are actually neighbours.
  std::vector<size_t> neighbourIndexes(permutationsVertexTouching.size());
  for (size_t i = 0; i < permutationsVertexTouching.size(); ++i) {

    size_t neighbour_index = m_pos + permutationsVertexTouching[i];
    neighbourIndexes[i] = neighbour_index;
    if (neighbour_index < m_ws->getNPoints() &&
        Utils::isNeighbourOfSubject(m_nd, neighbour_index, m_index, m_indexMaker, m_indexMax, widths)) {
      indexValidity[i] = true;
    }
  }

  return std::make_pair(neighbourIndexes, indexValidity);
}

/**
 *
 * @return The size of the permutation cache.
 */
size_t MDHistoWorkspaceIterator::permutationCacheSize() const { return m_permutationsVertexTouchingMap.size(); }

} // namespace Mantid::DataObjects