dice.c

/*----------------------------------------------------------------------------
 *
 * 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) 2008-2020, Euler Taveira de Oliveira
 *
 *----------------------------------------------------------------------------
 */

#include "similarity.h"
#include "tokenizer.h"


/* GUC variables */
int		pgs_dice_tokenizer = PGS_UNIT_ALNUM;
double	pgs_dice_threshold = 0.7f;
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);
}