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/*----------------------------------------------------------------------------
*
* block.c
*
* L1 distance or City Block distance or Manhattan distance
*
* Aims to measure the distance between two strings
*
* X is a list of n-grams
* Y is a list of n-grams
* T is a set of n-grams of X and/or Y
*
* For each n-gram in T we count occorrences in X and Y; we sum the
* absolute difference between nx and ny.
*
* For example:
*
* x: euler = {eu, ul, le, er}
* y: heuser = {he, eu, us, se, er}
* t: {eu, ul, le, er, he, us, se}
*
* eu ul le er he us se
* s = |1 - 1| + |1 - 0| + |1 - 0| + |1 - 1| + |0 - 1| + |0 - 1| + |0 - 1| = 5
*
* PS> we call n-grams: (i) n-sequence of letters (ii) n-sequence of words
*
* http://en.wikipedia.org/wiki/Block_distance
*
*
* Copyright (c) 2008-2018, Euler Taveira de Oliveira
*
*----------------------------------------------------------------------------
*/
#include "similarity.h"
#include "tokenizer.h"
/* GUC variables */
int pgs_block_tokenizer = PGS_UNIT_ALNUM;
double pgs_block_threshold = 0.7;
bool pgs_block_is_normalized = true;
PG_FUNCTION_INFO_V1(block);
Datum
block(PG_FUNCTION_ARGS)
{
char *a, *b;
TokenList *s, *t, *u;
Token *p, *q, *r;
int totpossible;
int totdistance;
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)));
/* lists */
s = initTokenList(0);
t = initTokenList(0);
/* set list */
u = initTokenList(1);
switch (pgs_block_tokenizer)
{
case PGS_UNIT_WORD:
tokenizeBySpace(s, a);
tokenizeBySpace(t, b);
/* all tokens in a set */
tokenizeBySpace(u, a);
tokenizeBySpace(u, b);
break;
case PGS_UNIT_GRAM:
tokenizeByGram(s, a);
tokenizeByGram(t, b);
/* all tokens in a set */
tokenizeByGram(u, a);
tokenizeByGram(u, b);
break;
case PGS_UNIT_CAMELCASE:
tokenizeByCamelCase(s, a);
tokenizeByCamelCase(t, b);
/* all tokens in a set */
tokenizeByCamelCase(u, a);
tokenizeByCamelCase(u, b);
break;
case PGS_UNIT_ALNUM: /* default */
default:
tokenizeByNonAlnum(s, a);
tokenizeByNonAlnum(t, b);
/* all tokens in a set */
tokenizeByNonAlnum(u, a);
tokenizeByNonAlnum(u, b);
break;
}
elog(DEBUG3, "Token List A");
printToken(s);
elog(DEBUG3, "Token List B");
printToken(t);
elog(DEBUG3, "All Token List");
printToken(u);
totpossible = s->size + t->size;
totdistance = 0;
p = u->head;
while (p != NULL)
{
int acnt = 0;
int bcnt = 0;
q = s->head;
while (q != NULL)
{
elog(DEBUG4, "p: %s; q: %s", p->data, q->data);
if (strcmp(p->data, q->data) == 0)
acnt++;
q = q->next;
}
r = t->head;
while (r != NULL)
{
elog(DEBUG4, "p: %s; r: %s", p->data, r->data);
if (strcmp(p->data, r->data) == 0)
bcnt++;
r = r->next;
}
if (acnt > bcnt)
totdistance += (acnt - bcnt);
else
totdistance += (bcnt - acnt);
elog(DEBUG2,
"\"%s\" => acnt(%d); bcnt(%d); totdistance(%d)",
p->data, acnt, bcnt, totdistance);
p = p->next;
}
elog(DEBUG1, "is normalized: %d", pgs_block_is_normalized);
elog(DEBUG1, "total possible: %d", totpossible);
elog(DEBUG1, "total distance: %d", totdistance);
destroyTokenList(s);
destroyTokenList(t);
destroyTokenList(u);
if (pgs_block_is_normalized)
res = (float8) (totpossible - totdistance) / totpossible;
else
res = totdistance;
PG_RETURN_FLOAT8(res);
}
PG_FUNCTION_INFO_V1(block_op);
Datum block_op(PG_FUNCTION_ARGS)
{
float8 res;
/*
* store *_is_normalized value temporarily 'cause
* threshold (we're comparing against) is normalized
*/
bool tmp = pgs_block_is_normalized;
pgs_block_is_normalized = true;
res = DatumGetFloat8(DirectFunctionCall2(
block,
PG_GETARG_DATUM(0),
PG_GETARG_DATUM(1)));
/* we're done; back to the previous value */
pgs_block_is_normalized = tmp;
PG_RETURN_BOOL(res >= pgs_block_threshold);
}
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