gini.cc

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/* gini.cc (Gini coefficient) */

/***********************************************************************
*  This code is part of Statistics for MySQL.
*
*  Copyright (C) 2015 Heinrich Schuchardt (xypron.glpk@gmx.de)
*
*  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.
***********************************************************************/


#include "sqlstat.h"
#include <set>

namespace sqlstat {

struct Item {
public:
  double x;
  double w;
};

struct ItemComperator {
public:
  bool operator() (const Item& left_item, const Item& right_item) const {
    return left_item.x < right_item.x;
  }
};

typedef std::multiset<Item, ItemComperator> ItemSet;

struct gini_storage {
  int argc;     
  ItemSet data; 
};

}

my_bool gini_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
  sqlstat::gini_storage *data;

  if (args->arg_count < 1 || args->arg_count > 2) {
    strcpy(message,"gini(x [,w]) requires one or two arguments");
    return 1;
  }
  args->arg_type[0] = REAL_RESULT;
  if (args->arg_count > 1) {
    args->arg_type[1] = REAL_RESULT;
  }

  data = new sqlstat::gini_storage();
  if (data == NULL) {
    strcpy(message,"Couldn't allocate memory");
    return 1;
  }
  data->argc = args->arg_count;

  initid->maybe_null = 1;
  initid->decimals   = NOT_FIXED_DEC;
  initid->max_length = 13 + initid->decimals;
  initid->ptr        = (char *) data;
  initid->const_item = 0;

  return 0;
}

void gini_reset(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
  gini_clear(initid, is_null, error);
  gini_add(initid, args, is_null, error);
}

void gini_clear(UDF_INIT *initid, char *is_null, char *error) {
  struct sqlstat::gini_storage *data;

  data = (struct sqlstat::gini_storage *) initid->ptr;
  data->data.clear();
}

void gini_add(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
  struct sqlstat::gini_storage *data;
  sqlstat::Item i;

  if (!args->args[0]) {
    return;
  }
  data = (struct sqlstat::gini_storage *) initid->ptr;
  i.x = *((double*) args->args[0]);
  if (data->argc > 1 && args->args[1]) {
    i.w = *((double*) args->args[1]);
  } else {
    i.w = 1;
  }
  try {
    data->data.insert(i);
  } catch (std::bad_alloc e) {
    *error = 1;
  }
}

double gini(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
  struct sqlstat::gini_storage *data;
  sqlstat::ItemSet::iterator pos;

  double sumx = 0;
  double sumw = 0;
  double ret = 0;

  data = (struct sqlstat::gini_storage *) initid->ptr;

  for(pos = data->data.begin(); pos != data->data.end(); ++pos) {
    double w = (*pos).w;
    double x = w * (*pos).x;
    ret += w * (2. * sumx + x);
    sumx += x;
    sumw += w;
  }

  if (sumx == 0 || sumw == 0) {
    *is_null = 1;
    return 0;
  }

  return 1. - ret / (sumx * sumw);
}

void gini_deinit(UDF_INIT *initid) {
  struct sqlstat::gini_storage *data;
  if (initid->ptr) {
    data = (struct sqlstat::gini_storage *) initid->ptr;
    delete data;
  }
}