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#include <math.h>
#include <assert.h>
#include "sqlite3.h"
static void okapi_bm25(sqlite3_context *pCtx, int nVal, sqlite3_value **apVal) {
assert(sizeof(int) == 4);
const unsigned int *matchinfo = (const unsigned int *)sqlite3_value_blob(apVal[0]);
int searchTextCol = sqlite3_value_int(apVal[1]);
double K1 = ((nVal >= 3) ? sqlite3_value_double(apVal[2]) : 1.2);
double B = ((nVal >= 4) ? sqlite3_value_double(apVal[3]) : 0.75);
int P_OFFSET = 0;
int C_OFFSET = 1;
int X_OFFSET = 2;
int termCount = matchinfo[P_OFFSET];
int colCount = matchinfo[C_OFFSET];
int N_OFFSET = X_OFFSET + 3*termCount*colCount;
int A_OFFSET = N_OFFSET + 1;
int L_OFFSET = (A_OFFSET + colCount);
double totalDocs = matchinfo[N_OFFSET];
double avgLength = matchinfo[A_OFFSET + searchTextCol];
double docLength = matchinfo[L_OFFSET + searchTextCol];
double sum = 0.0;
for (int i = 0; i < termCount; i++) {
int currentX = X_OFFSET + (3 * searchTextCol * (i + 1));
double termFrequency = matchinfo[currentX];
double docsWithTerm = matchinfo[currentX + 2];
double idf = log(
(totalDocs - docsWithTerm + 0.5) /
(docsWithTerm + 0.5)
);
double rightSide = (
(termFrequency * (K1 + 1)) /
(termFrequency + (K1 * (1 - B + (B * (docLength / avgLength)))))
);
sum += (idf * rightSide);
}
sqlite3_result_double(pCtx, sum);
}
//
// Created by Joshua Wilson on 27/05/14.
// Copyright (c) 2014 Joshua Wilson. All rights reserved.
// https://github.com/neozenith/sqlite-okapi-bm25
//
// This is an extension to the work of "Radford 'rads' Smith"
// found at: https://github.com/rads/sqlite-okapi-bm25
// which is covered by the MIT License
// http://opensource.org/licenses/MIT
// the following code shall also be covered by the same MIT License
static void okapi_bm25f(sqlite3_context *pCtx, int nVal, sqlite3_value **apVal) {
assert(sizeof(int) == 4);
const unsigned int *matchinfo = (const unsigned int *)sqlite3_value_blob(apVal[0]);
//Setting the default values and ignoring argument based inputs so the extra
//arguments can be the column weights instead.
double K1 = 1.2;// ((nVal >= 3) ? sqlite3_value_double(apVal[2]) : 1.2);
double B = 0.75;// ((nVal >= 4) ? sqlite3_value_double(apVal[3]) : 0.75);
//For a good explanation fo the maths and how to choose these variables
//http://stackoverflow.com/a/23161886/622276
//NOTE: the rearranged order of parameters to match the order presented on
//SQLite3 FTS3 documentation 'pcxnals' (http://www.sqlite.org/fts3.html#matchinfo)
int P_OFFSET = 0;
int C_OFFSET = 1;
int X_OFFSET = 2;
int termCount = matchinfo[P_OFFSET];
int colCount = matchinfo[C_OFFSET];
int N_OFFSET = X_OFFSET + 3*termCount*colCount;
int A_OFFSET = N_OFFSET + 1;
int L_OFFSET = (A_OFFSET + colCount);
// int S_OFFSET = (L_OFFSET + colCount); //useful as a pseudo proximity weighting per field/column
double totalDocs = matchinfo[N_OFFSET];
double avgLength = 0.0;
double docLength = 0.0;
for (int col = 0; col < colCount; col++)
{
avgLength += matchinfo[A_OFFSET + col];
docLength += matchinfo[L_OFFSET + col];
}
double epsilon = 1.0 / (totalDocs*avgLength);
double sum = 0.0;
for (int t = 0; t < termCount; t++) {
for (int col = 0 ; col < colCount; col++)
{
int currentX = X_OFFSET + (3 * col * (t + 1));
double termFrequency = matchinfo[currentX];
double docsWithTerm = matchinfo[currentX + 2];
double idf = log(
(totalDocs - docsWithTerm + 0.5) /
(docsWithTerm + 0.5)
);
// "...terms appearing in more than half of the corpus will provide negative contributions to the final document score."
//http://en.wikipedia.org/wiki/Okapi_BM25
idf = (idf < 0) ? epsilon : idf; //common terms could have no effect (\epsilon=0.0) or a very small effect (\epsilon=1/NoOfTokens which asymptotes to 0.0)
double rightSide = (
(termFrequency * (K1 + 1)) /
(termFrequency + (K1 * (1 - B + (B * (docLength / avgLength)))))
);
rightSide += 1.0;
//To comply with BM25+ that solves a lower bounding issue where large documents that match are unfairly scored as
//having similar relevancy as short documents that do not contain as many terms
//Yuanhua Lv and ChengXiang Zhai. 'Lower-bounding term frequency normalization.' In Proceedings of CIKM'2011, pages 7-16.
//http://sifaka.cs.uiuc.edu/~ylv2/pub/cikm11-lowerbound.pdf
double weight = ((nVal > col+1) ? sqlite3_value_double(apVal[col+1]) : 1.0);
// double subsequence = matchinfo[S_OFFSET + col];
sum += (idf * rightSide) * weight; // * subsequence; //useful as a pseudo proximty weighting
}
}
sqlite3_result_double(pCtx, sum);
}
static void okapi_bm25f_kb(sqlite3_context *pCtx, int nVal, sqlite3_value **apVal) {
assert(sizeof(int) == 4);
const unsigned int *matchinfo = (const unsigned int *)sqlite3_value_blob(apVal[0]);
//Setting the default values and ignoring argument based inputs so the extra
//arguments can be the column weights instead.
if (nVal < 2) sqlite3_result_error(pCtx, "wrong number of arguments to function okapi_bm25_kb(), expected k1 parameter", -1);
if (nVal < 3) sqlite3_result_error(pCtx, "wrong number of arguments to function okapi_bm25_kb(), expected b parameter", -1);
double K1 = sqlite3_value_double(apVal[1]);
double B = sqlite3_value_double(apVal[2]);
//For a good explanation fo the maths and how to choose these variables
//http://stackoverflow.com/a/23161886/622276
//NOTE: the rearranged order of parameters to match the order presented on
//SQLite3 FTS3 documentation 'pcxnals' (http://www.sqlite.org/fts3.html#matchinfo)
int P_OFFSET = 0;
int C_OFFSET = 1;
int X_OFFSET = 2;
int termCount = matchinfo[P_OFFSET];
int colCount = matchinfo[C_OFFSET];
int N_OFFSET = X_OFFSET + 3*termCount*colCount;
int A_OFFSET = N_OFFSET + 1;
int L_OFFSET = (A_OFFSET + colCount);
// int S_OFFSET = (L_OFFSET + colCount); //useful as a pseudo proximity weighting per field/column
double totalDocs = matchinfo[N_OFFSET];
double avgLength = 0.0;
double docLength = 0.0;
for (int col = 0; col < colCount; col++)
{
avgLength += matchinfo[A_OFFSET + col];
docLength += matchinfo[L_OFFSET + col];
}
double epsilon = 1.0 / (totalDocs*avgLength);
double sum = 0.0;
for (int t = 0; t < termCount; t++) {
for (int col = 0 ; col < colCount; col++)
{
int currentX = X_OFFSET + (3 * col * (t + 1));
double termFrequency = matchinfo[currentX];
double docsWithTerm = matchinfo[currentX + 2];
double idf = log(
(totalDocs - docsWithTerm + 0.5) /
(docsWithTerm + 0.5)
);
// "...terms appearing in more than half of the corpus will provide negative contributions to the final document score."
//http://en.wikipedia.org/wiki/Okapi_BM25
idf = (idf < 0) ? epsilon : idf; //common terms could have no effect (\epsilon=0.0) or a very small effect (\epsilon=1/NoOfTokens which asymptotes to 0.0)
double rightSide = (
(termFrequency * (K1 + 1)) /
(termFrequency + (K1 * (1 - B + (B * (docLength / avgLength)))))
);
rightSide += 1.0;
//To comply with BM25+ that solves a lower bounding issue where large documents that match are unfairly scored as
//having similar relevancy as short documents that do not contain as many terms
//Yuanhua Lv and ChengXiang Zhai. 'Lower-bounding term frequency normalization.' In Proceedings of CIKM'2011, pages 7-16.
//http://sifaka.cs.uiuc.edu/~ylv2/pub/cikm11-lowerbound.pdf
double weight = ((nVal > col+3) ? sqlite3_value_double(apVal[col+3]) : 1.0);
// double subsequence = matchinfo[S_OFFSET + col];
sum += (idf * rightSide) * weight; // * subsequence; //useful as a pseudo proximty weighting
}
}
sqlite3_result_double(pCtx, sum);
}
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