Interp 函数示例

Interp 函数是使用时间系列 API 的服务器函数的示例。此函数在规则时间系列的值之间插入值以填充空元素。

此函数不处理单个空列。它假设所有列都属于 FLOAT 类型。

Interp 可按以下方式使用：
select Interp(stock_data) from daily_stocks where stock_name = 'GBase';

此示例和许多其他示例都在 $GBASEDBTDIR/extend/TimeSeries.version 目录中提供。

要使用 Interp 函数，请创建服务器函数：
create function Interp(TimeSeries) returns TimeSeries
external name '/tmp/Interpolate.bld(ts_interp)'
language c not variant;
现在可以在 DB-Access 语句中使用 Interp 函数。示例如下，但请注意以下两个查询之间的输出差异（输出已重新格式化；您看到的实际输出将不采用表格格式）：
select stock_data from daily_stocks where stock_name = 'GBase';


2011-01-03 00:00:00    1   1   1   1
2011-01-04 00:00:00    2   2   2   2
NULL
2011-01-06 00:00:00    3   3   3   3


select Interp(stock_data) from daily_stocks where stock_name = 'GBase';

2011-01-03 00:00:00    1   1   1   1
2011-01-04 00:00:00    2   2   2   2
2011-01-05 00:00:00    2.5 2.5 2.5 2.5
2011-01-06 00:00:00    3   3   3   3
/* 
 * SETUP:
 * create function Interp(TimeSeries) returns TimeSeries
 * external name 'Interpolate.so(ts_interp)'
 * language c not variant;
 * 
 *
 * USAGE:
 * select Interp(stock_data) from daily_stocks where stock_id = 901;
 */

#include <stdio.h>
#include <mi.h>
#include <tseries.h>

# define TS_MAX_COLS   100
# define DATATYPE   "smallfloat"

/*
 * This example interpolates between values to fill in null elements.
 * It assumes that all columns are of type smallfloat and that there
are 
 * less than 100 columns in each element.
 */

ts_timeseries *
ts_interp(tsPtr, fParamPtr)
    ts_timeseries   *tsPtr;
    MI_FPARAM      *fParamPtr;
{
    ts_tsdesc      *descPtr;
    ts_tselem      tselem;
    ts_tscan      *scan;
    MI_CONNECTION       *conn;
    ts_typeinfo      *typeinfo;
    int         scancode;
    mi_real           *values[TS_MAX_COLS];
    mi_real           lastValues[TS_MAX_COLS], newValues[TS_MAX_COLS];
    mi_boolean      nulls[TS_MAX_COLS];
    mi_integer      minElem, curElem, elem;
    mi_integer     i;
    mi_boolean      noneYet;
    mi_integer      ncols;
    char      strbuf[100];
    
    /* get a connection for libmi */
    conn = mi_open(NULL,NULL,NULL);

    /* open a descriptor for the timeseries */
    descPtr = ts_open(conn, tsPtr, mi_fp_rettype(fParamPtr, 0), 0);

    if ((ncols = (mi_integer) mi_fp_funcstate(fParamPtr)) == 0) {
   ncols = ts_col_cnt(descPtr);

   if (ncols > TS_MAX_COLS) {
       sprintf(strbuf, "Timeseries elements have too many columns,
100 is 
the max, got %d instead.", ncols);
       mi_db_error_raise(NULL, MI_FATAL, strbuf, 0);
   }

   for (i = 1; i < ncols; i++) {
       typeinfo = ts_colinfo_number(descPtr, i);

       if (strlen(typeinfo->ti_typename) != strlen(DATATYPE) &&
      memcmp(typeinfo->ti_typename, DATATYPE, strlen(DATATYPE)) !=
0){
      sprintf(strbuf, "column was not a %s, got %s instead.", DATATYPE,

typeinfo->ti_typename);
      mi_db_error_raise(NULL, MI_FATAL, strbuf, 0);
       }
   }

   mi_fp_setfuncstate(fParamPtr, (void *) ncols);
    }

    noneYet = MI_TRUE;
    minElem = -1;
    curElem = 0;
    /* begin a scan of the whole timeseries */
    scan = ts_begin_scan(descPtr, 0, NULL, NULL);
    while ((scancode = ts_next(scan, &tselem)) != TS_SCAN_EOS)
{
   switch(scancode) {
       case TS_SCAN_ELEM:
      /* if this element is not null expand its values */
      noneYet = MI_FALSE;
      ts_get_all_cols(descPtr, tselem, (void **) values, nulls, curElem);
      if (minElem == -1) {
          /* save each element */
          for (i = 1; i < ncols; i++) 
         lastValues[i] = *values[i];
      }
      else {
          /* calculate the average */
          for (i = 1; i < ncols; i++) {
         newValues[i] = (*values[i] + lastValues[i])/2.0;
         lastValues[i] = *values[i];
         values[i] = &newValues[i];
          }

          /* update the missing elements */

          tselem = ts_make_elem(descPtr, (void **) values, nulls, &elem);
          for (elem = minElem; elem < curElem; elem++)
         ts_put_nth_elem(descPtr, tselem, elem);

          minElem = -1;
      }
          
      break;
       case TS_SCAN_NULL:
      if (noneYet) 
          break;
      /* remember the first null element */
      if (minElem == -1)
          minElem = curElem;
      break;
   }

   curElem++;
    }
    ts_end_scan(scan);
    ts_close(descPtr);
    return(tsPtr);
}