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/*----------------------------------------------------------------------------
*
* dice.c
*
* Dice's coefficient is a similarity measure
*
* 2 * nt
* s = ---------
* nx + ny
*
* where nt is the number of n-grams found in both strings, nx is the
* number of n-grams in x and, ny is the number of n-grams in y.
*
* For example:
*
* x: euler = {eu, ul, le, er}
* y: heuser = {he, eu, us, se, er}
*
* 2*nt 2 * 2
* s = --------- = ------- = 0.4444...
* nx + ny 4 + 5
*
* PS> we call n-grams: (i) n-sequence of letters (ii) n-sequence of words
*
*
* Copyright (c) 2008-2018, Euler Taveira de Oliveira
*
*----------------------------------------------------------------------------
*/
#include "similarity.h"
#include "tokenizer.h"
/* GUC variables */
int pgs_dice_tokenizer = PGS_UNIT_ALNUM;
double pgs_dice_threshold = 0.7;
bool pgs_dice_is_normalized = true;
PG_FUNCTION_INFO_V1(dice);
Datum
dice(PG_FUNCTION_ARGS)
{
char *a, *b;
TokenList *s, *t;
int atok, btok, comtok, alltok;
float8 res;
a = DatumGetPointer(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(0))));
b = DatumGetPointer(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(1))));
if (strlen(a) > PGS_MAX_STR_LEN || strlen(b) > PGS_MAX_STR_LEN)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("argument exceeds the maximum length of %d bytes",
PGS_MAX_STR_LEN)));
/* sets */
s = initTokenList(1);
t = initTokenList(1);
switch (pgs_dice_tokenizer)
{
case PGS_UNIT_WORD:
tokenizeBySpace(s, a);
tokenizeBySpace(t, b);
break;
case PGS_UNIT_GRAM:
tokenizeByGram(s, a);
tokenizeByGram(t, b);
break;
case PGS_UNIT_CAMELCASE:
tokenizeByCamelCase(s, a);
tokenizeByCamelCase(t, b);
break;
case PGS_UNIT_ALNUM: /* default */
default:
tokenizeByNonAlnum(s, a);
tokenizeByNonAlnum(t, b);
break;
}
elog(DEBUG3, "Token List A");
printToken(s);
elog(DEBUG3, "Token List B");
printToken(t);
atok = s->size;
btok = t->size;
/* combine the sets */
switch (pgs_dice_tokenizer)
{
case PGS_UNIT_WORD:
tokenizeBySpace(s, b);
break;
case PGS_UNIT_GRAM:
tokenizeByGram(s, b);
break;
case PGS_UNIT_CAMELCASE:
tokenizeByCamelCase(s, b);
break;
case PGS_UNIT_ALNUM: /* default */
default:
tokenizeByNonAlnum(s, b);
break;
}
elog(DEBUG3, "All Token List");
printToken(s);
alltok = s->size;
destroyTokenList(s);
destroyTokenList(t);
comtok = atok + btok - alltok;
elog(DEBUG1, "is normalized: %d", pgs_dice_is_normalized);
elog(DEBUG1, "token list A size: %d", atok);
elog(DEBUG1, "token list B size: %d", btok);
elog(DEBUG1, "all tokens size: %d", alltok);
elog(DEBUG1, "common tokens size: %d", comtok);
/* normalized and unnormalized version are the same */
res = (float8) (2.0 * comtok) / (atok + btok);
PG_RETURN_FLOAT8(res);
}
PG_FUNCTION_INFO_V1(dice_op);
Datum dice_op(PG_FUNCTION_ARGS)
{
float8 res;
/*
* store *_is_normalized value temporarily 'cause
* threshold (we're comparing against) is normalized
*/
bool tmp = pgs_dice_is_normalized;
pgs_dice_is_normalized = true;
res = DatumGetFloat8(DirectFunctionCall2(
dice,
PG_GETARG_DATUM(0),
PG_GETARG_DATUM(1)));
/* we're done; back to the previous value */
pgs_dice_is_normalized = tmp;
PG_RETURN_BOOL(res >= pgs_dice_threshold);
}
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