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udf_median.cc
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udf_median.cc
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/*
returns the median of the values in a distribution
input parameters:
data (real)
number of decimals in result (int, optional)
output:
median value of the distribution (real)
registering the function:
CREATE AGGREGATE FUNCTION median RETURNS REAL SONAME 'udf_median.so';
getting rid of the function:
DROP FUNCTION median;
04/15/2009
- added percentile, an optional third parameter median function
- default percentile is 50 (for the standard median)
*/
#ifdef STANDARD
#include <stdio.h>
#include <string.h>
#ifdef __WIN__
typedef unsigned __int64 ulonglong;
typedef __int64 longlong;
#else
typedef unsigned long long ulonglong;
typedef long long longlong;
#endif /*__WIN__*/
#else
#include <my_global.h>
#include <my_sys.h>
#endif
#include <mysql.h>
#include <m_ctype.h>
#include <m_string.h>
/*#ifdef HAVE_DLOPEN*/
#define BUFFERSIZE 1024
extern "C" {
my_bool median_init( UDF_INIT* initid, UDF_ARGS* args, char* message );
void median_deinit( UDF_INIT* initid );
void median_clear( UDF_INIT* initid, char* is_null, char *error );
void median_reset( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error );
void median_add( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error );
double median( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error );
}
struct median_data
{
unsigned long count;
unsigned long abscount;
unsigned long pages;
unsigned long percentile;
double *values;
};
my_bool median_init( UDF_INIT* initid, UDF_ARGS* args, char* message )
{
if (args->arg_count < 1 || args->arg_count>3)
{
strcpy(message,"wrong number of arguments: median() requires one or two arguments");
return 1;
}
if (args->arg_type[0]!=REAL_RESULT)
{
/* strcpy(message,"median() requires a real as parameter 1");
return 1; */
args->arg_type[0] = REAL_RESULT;
}
if (args->arg_count>1 && (args->arg_type[1]!=INT_RESULT))
{
strcpy(message,"median() requires an int as parameter 2");
return 1;
}
initid->decimals=2;
if (args->arg_count==2 && (*((ulong*)args->args[1])<=16))
{
initid->decimals=*((ulong*)args->args[1]);
}
/* Default median percentage is 50% */
unsigned long percentile=50;
if (args->arg_count==3 && (*((ulong*)args->args[2])>=0) && (*((ulong*)args->args[2])<=100))
{
percentile=*((ulong*)args->args[2]);
}
median_data *buffer = new median_data;
buffer->count = 0;
buffer->abscount=0;
buffer->pages = 1;
buffer->values = NULL;
buffer->percentile=percentile;
initid->maybe_null = 1;
initid->max_length = 32;
initid->ptr = (char*)buffer;
return 0;
}
void median_deinit( UDF_INIT* initid )
{
median_data *buffer = (median_data*)initid->ptr;
if (buffer->values != NULL)
{
free(buffer->values);
buffer->values=NULL;
}
delete initid->ptr;
}
void median_clear( UDF_INIT* initid, char* is_null, char* is_error )
{
median_data *buffer = (median_data*)initid->ptr;
buffer->count = 0;
buffer->abscount=0;
buffer->pages = 1;
*is_null = 0;
*is_error = 0;
if (buffer->values != NULL)
{
free(buffer->values);
buffer->values=NULL;
}
buffer->values=(double *) malloc(BUFFERSIZE*sizeof(double));
}
void median_reset( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char* is_error )
{
median_clear(initid, is_null, is_error);
median_add( initid, args, is_null, is_error );
}
void median_add( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char* is_error )
{
if (args->args[0]!=NULL)
{
median_data *buffer = (median_data*)initid->ptr;
if (buffer->count>=BUFFERSIZE)
{
buffer->pages++;
buffer->count=0;
buffer->values=(double *) realloc(buffer->values,BUFFERSIZE*buffer->pages*sizeof(double));
}
buffer->values[buffer->abscount++] = *((double*)args->args[0]);
buffer->count++;
}
}
int
compare_doubles (const void *a, const void *b)
{
const double *da = (const double *) a;
const double *db = (const double *) b;
return (*da > *db) - (*da < *db);
}
double median( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char* is_error )
{
median_data* buffer = (median_data*)initid->ptr;
if (buffer->abscount==0 || *is_error!=0)
{
*is_null = 1;
return 0.0;
}
*is_null=0;
if (buffer->abscount==1)
{
return buffer->values[0];
}
qsort(buffer->values,buffer->abscount,sizeof(double),compare_doubles);
unsigned long bufindex = (ulong) ((((double)buffer->abscount - 1.0) * (double)buffer->percentile) / 100.0);
return buffer->values[bufindex];
}
/* #endif */