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      1 // Ceres Solver - A fast non-linear least squares minimizer
      2 // Copyright 2012 Google Inc. All rights reserved.
      3 // http://code.google.com/p/ceres-solver/
      4 //
      5 // Redistribution and use in source and binary forms, with or without
      6 // modification, are permitted provided that the following conditions are met:
      7 //
      8 // * Redistributions of source code must retain the above copyright notice,
      9 //   this list of conditions and the following disclaimer.
     10 // * Redistributions in binary form must reproduce the above copyright notice,
     11 //   this list of conditions and the following disclaimer in the documentation
     12 //   and/or other materials provided with the distribution.
     13 // * Neither the name of Google Inc. nor the names of its contributors may be
     14 //   used to endorse or promote products derived from this software without
     15 //   specific prior written permission.
     16 //
     17 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
     18 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     19 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     20 // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
     21 // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     22 // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     23 // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     24 // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     25 // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     26 // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     27 // POSSIBILITY OF SUCH DAMAGE.
     28 //
     29 // Author: sameeragarwal (at) google.com (Sameer Agarwal)
     30 
     31 #ifndef CERES_PUBLIC_ORDERED_GROUPS_H_
     32 #define CERES_PUBLIC_ORDERED_GROUPS_H_
     33 
     34 #include <map>
     35 #include <set>
     36 #include "ceres/internal/port.h"
     37 
     38 namespace ceres {
     39 
     40 // A class for storing and manipulating an ordered collection of
     41 // groups/sets with the following semantics:
     42 //
     43 // Group ids are non-negative integer values. Elements are any type
     44 // that can serve as a key in a map or an element of a set.
     45 //
     46 // An element can only belong to one group at a time. A group may
     47 // contain an arbitrary number of elements.
     48 //
     49 // Groups are ordered by their group id.
     50 template <typename T>
     51 class OrderedGroups {
     52  public:
     53   // Add an element to a group. If a group with this id does not
     54   // exist, one is created. This method can be called any number of
     55   // times for the same element. Group ids should be non-negative
     56   // numbers.
     57   //
     58   // Return value indicates if adding the element was a success.
     59   bool AddElementToGroup(const T element, const int group) {
     60     if (group < 0) {
     61       return false;
     62     }
     63 
     64     typename map<T, int>::const_iterator it = element_to_group_.find(element);
     65     if (it != element_to_group_.end()) {
     66       if (it->second == group) {
     67         // Element is already in the right group, nothing to do.
     68         return true;
     69       }
     70 
     71       group_to_elements_[it->second].erase(element);
     72       if (group_to_elements_[it->second].size() == 0) {
     73         group_to_elements_.erase(it->second);
     74       }
     75     }
     76 
     77     element_to_group_[element] = group;
     78     group_to_elements_[group].insert(element);
     79     return true;
     80   }
     81 
     82   void Clear() {
     83     group_to_elements_.clear();
     84     element_to_group_.clear();
     85   }
     86 
     87   // Remove the element, no matter what group it is in. If the element
     88   // is not a member of any group, calling this method will result in
     89   // a crash.
     90   //
     91   // Return value indicates if the element was actually removed.
     92   bool Remove(const T element) {
     93     const int current_group = GroupId(element);
     94     if (current_group < 0) {
     95       return false;
     96     }
     97 
     98     group_to_elements_[current_group].erase(element);
     99 
    100     if (group_to_elements_[current_group].size() == 0) {
    101       // If the group is empty, then get rid of it.
    102       group_to_elements_.erase(current_group);
    103     }
    104 
    105     element_to_group_.erase(element);
    106     return true;
    107   }
    108 
    109   // Reverse the order of the groups in place.
    110   void Reverse() {
    111     typename map<int, set<T> >::reverse_iterator it =
    112         group_to_elements_.rbegin();
    113     map<int, set<T> > new_group_to_elements;
    114     new_group_to_elements[it->first] = it->second;
    115 
    116     int new_group_id = it->first + 1;
    117     for (++it; it != group_to_elements_.rend(); ++it) {
    118       for (typename set<T>::const_iterator element_it = it->second.begin();
    119            element_it != it->second.end();
    120            ++element_it) {
    121         element_to_group_[*element_it] = new_group_id;
    122       }
    123       new_group_to_elements[new_group_id] = it->second;
    124       new_group_id++;
    125     }
    126 
    127     group_to_elements_.swap(new_group_to_elements);
    128   }
    129 
    130   // Return the group id for the element. If the element is not a
    131   // member of any group, return -1.
    132   int GroupId(const T element) const {
    133     typename map<T, int>::const_iterator it = element_to_group_.find(element);
    134     if (it == element_to_group_.end()) {
    135       return -1;
    136     }
    137     return it->second;
    138   }
    139 
    140   bool IsMember(const T element) const {
    141     typename map<T, int>::const_iterator it = element_to_group_.find(element);
    142     return (it != element_to_group_.end());
    143   }
    144 
    145   // This function always succeeds, i.e., implicitly there exists a
    146   // group for every integer.
    147   int GroupSize(const int group) const {
    148     typename map<int, set<T> >::const_iterator it =
    149         group_to_elements_.find(group);
    150     return (it ==  group_to_elements_.end()) ? 0 : it->second.size();
    151   }
    152 
    153   int NumElements() const {
    154     return element_to_group_.size();
    155   }
    156 
    157   // Number of groups with one or more elements.
    158   int NumGroups() const {
    159     return group_to_elements_.size();
    160   }
    161 
    162   const map<int, set<T> >& group_to_elements() const {
    163     return group_to_elements_;
    164   }
    165 
    166  private:
    167   map<int, set<T> > group_to_elements_;
    168   map<T, int> element_to_group_;
    169 };
    170 
    171 // Typedef for the most commonly used version of OrderedGroups.
    172 typedef OrderedGroups<double*> ParameterBlockOrdering;
    173 
    174 }  // namespace ceres
    175 
    176 #endif  // CERES_PUBLIC_ORDERED_GROUP_H_
    177