Statistics for MySQL  0.9
median.cc
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00001 /* median.cc (median) */
00002 
00003 /***********************************************************************
00004 *  This code is part of Statistics for MySQL.
00005 *
00006 *  Copyright (C) 2011 Heinrich Schuchardt (xypron.glpk@gmx.de)
00007 *
00008 *  Licensed under the Apache License, Version 2.0 (the "License");
00009 *  you may not use this file except in compliance with the License.
00010 *  You may obtain a copy of the License at
00011 *
00012 *      http://www.apache.org/licenses/LICENSE-2.0
00013 *
00014 *  Unless required by applicable law or agreed to in writing, software
00015 *  distributed under the License is distributed on an "AS IS" BASIS,
00016 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00017 *  See the License for the specific language governing permissions and
00018 *  limitations under the License.
00019 ***********************************************************************/
00020 
00021 
00031 #include "sqlstat.h"
00032 #include <set>
00033 
00034 using namespace std;
00035 
00039 typedef multiset<double, less<double> > DoubleSet;
00040 
00053 my_bool median_init(UDF_INIT *initid, UDF_ARGS *args, char *message) {
00054   DoubleSet *data;
00055   
00056   if (args->arg_count != 1) {
00057     strcpy(message,"median() requires one argument");
00058     return 1;
00059   }
00060   args->arg_type[0] = REAL_RESULT;
00061 
00062   data = new DoubleSet();
00063   if (data == NULL) {
00064     strcpy(message,"Couldn't allocate memory");
00065     return 1;
00066   }  
00067   
00068   initid->maybe_null = 1;
00069   initid->decimals   = NOT_FIXED_DEC;
00070   initid->max_length = 13 + initid->decimals;
00071   initid->ptr        = (char *) data;
00072   initid->const_item = 0;
00073   
00074   return 0;
00075 }
00076 
00088 void median_reset(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
00089   median_clear(initid, is_null, error);
00090   median_add(initid, args, is_null, error);
00091 }
00092 
00102 void median_clear(UDF_INIT *initid, char *is_null, char *error) {
00103   DoubleSet *data;
00104 
00105   data = (DoubleSet *) initid->ptr;
00106   data->clear();
00107 }
00108 
00119 void median_add(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
00120   DoubleSet *data;
00121   double x;
00122   
00123   if (!args->args[0]) {
00124     return;
00125   }
00126   data = (DoubleSet *) initid->ptr;
00127   x = *((double*) args->args[0]);
00128 
00129   data->insert(x);
00130 }
00131 
00141 double median(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error) {
00142   DoubleSet *data;
00143   DoubleSet::iterator pos;
00144   double ret;
00145   size_t n;
00146   size_t n2;
00147 
00148   data = (DoubleSet *) initid->ptr;
00149 
00150   
00151   n = data->size();
00152   if (n <= 0 ) {
00153     *is_null = 1;
00154     return 0;
00155   }
00156 
00157   n2 = ++n / 2;
00158 
00159   pos = data->begin();
00160   for (int i = 0; i < n2; i++) {
00161     ret = *pos++;
00162   }
00163 
00164   if (1 & n) {
00165     ret += *pos;
00166     ret /= 2;
00167   }
00168   
00169   return ret;
00170 }
00171 
00179 void median_deinit(UDF_INIT *initid) {
00180   DoubleSet *data;
00181   if (initid->ptr) {
00182     data = (DoubleSet *) initid->ptr;
00183     data->~multiset();
00184   }
00185 }
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