median.cc

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/* median.cc (median) */

/***********************************************************************
*  This code is part of Statistics for MySQL.
*
*  Copyright (C) 2011 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>

using namespace std;

typedef multiset<double, less<double> > DoubleSet;

my_bool median_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
  DoubleSet *data;

  if (args->arg_count != 1) {
    strcpy(message,"median() requires one argument");
    return 1;
  }
  args->arg_type[0] = REAL_RESULT;

  data = new DoubleSet();
  if (data == NULL) {
    strcpy(message,"Couldn't allocate memory");
    return 1;
  }

  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 median_reset(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
  median_clear(initid, is_null, error);
  median_add(initid, args, is_null, error);
}

void median_clear(UDF_INIT *initid, char *is_null, char *error) {
  DoubleSet *data;

  data = (DoubleSet *) initid->ptr;
  data->clear();
}

void median_add(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
  DoubleSet *data;
  double x;

  if (!args->args[0]) {
    return;
  }
  data = (DoubleSet *) initid->ptr;
  x = *((double*) args->args[0]);

  try {
    data->insert(x);
  } catch (std::bad_alloc e) {
    *error = 1;
  }
}

double median(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
  DoubleSet *data;
  DoubleSet::iterator pos;
  double ret;
  size_t n;
  size_t n2;

  data = (DoubleSet *) initid->ptr;


  n = data->size();
  if (n <= 0 ) {
    *is_null = 1;
    return 0;
  }

  n2 = ++n / 2;

  pos = data->begin();
  for (size_t i = 0; i < n2; i++) {
    ret = *pos++;
  }

  if (1 & n) {
    ret += *pos;
    ret /= 2;
  }

  return ret;
}

void median_deinit(UDF_INIT *initid) {
  DoubleSet *data;
  if (initid->ptr) {
    data = (DoubleSet *) initid->ptr;
    data->~multiset();
  }
}