m_ndcg2.c

/*
 Copyright (c) 2008 - Chris Buckley.
 Copyright (c) 2016 - Daniel Valcarce.

 Permission is granted for use and modification of this file for
 research, non-commercial purposes.
 */

#include "common.h"
#include "sysfunc.h"
#include "trec_eval.h"
#include "functions.h"
#include "trec_format.h"
double log2(double x);

static int
te_calc_ndcg2(const EPI *epi, const REL_INFO *rel_info, const RESULTS *results,
		const TREC_MEAS *tm, TREC_EVAL *eval);
static PARAMS default_ndcg2_gains = { NULL, 0, NULL };

/* See trec_eval.h for definition of TREC_MEAS */
TREC_MEAS te_meas_ndcg2 =
		{ "ndcg2",
				"    Normalized Discounted Cumulative Gain 2\n\
		Compute the nDCG measure using 2^rel_level gains.\n\
		Based on Ian Soboroff implementation.\n",
				te_init_meas_s_float_p_pair, te_calc_ndcg2, te_acc_meas_s,
				te_calc_avg_meas_s, te_print_single_meas_s_float,
				te_print_final_meas_s_float_p, &default_ndcg2_gains, -1 };

/* Keep track of valid rel_levels and associated gains */
/* Initialized in setup_gains */
typedef struct {
	long rel_level;
	long num_at_level;
	double gain;
} REL_GAIN;

typedef struct {
	REL_GAIN *rel_gains;
	long num_gains;
	long total_num_at_levels;
} GAINS;

static int setup_gains(const TREC_MEAS *tm, const RES_RELS *res_rels,
		GAINS *gains);
static double get_gain(const long rel_level, const GAINS *gains);
static int comp_rel_gain();

static int te_calc_ndcg2(const EPI *epi, const REL_INFO *rel_info,
		const RESULTS *results, const TREC_MEAS *tm, TREC_EVAL *eval) {
	RES_RELS res_rels;
	double results_gain, results_dcg;
	double ideal_gain, ideal_dcg;
	long cur_level, num_at_level;
	long i;
	GAINS gains;

	if (UNDEF == te_form_res_rels(epi, rel_info, results, &res_rels))
		return (UNDEF);

	if (UNDEF == setup_gains(tm, &res_rels, &gains))
		return (UNDEF);

	results_dcg = 0.0;
	ideal_dcg = 0.0;
	cur_level = gains.num_gains - 1;
	ideal_gain = (cur_level >= 0) ? gains.rel_gains[cur_level].gain : 0.0;
	num_at_level = 0;

	for (i = 0; i < res_rels.num_ret && ideal_gain > 0.0; i++) {
		/* Calculate change in results dcg */
		results_gain = get_gain(res_rels.results_rel_list[i], &gains);
		if (results_gain != 0)
			/* Note: i+2 since doc i has rank i+1 */
			results_dcg += results_gain / log2((double) (i + 2));
		/* Calculate change in ideal dcg */
		num_at_level++;
		while (cur_level >= 0
				&& num_at_level > gains.rel_gains[cur_level].num_at_level) {
			num_at_level = 1;
			cur_level--;
			ideal_gain =
					(cur_level >= 0) ? gains.rel_gains[cur_level].gain : 0.0;
		}
		if (ideal_gain > 0.0)
			ideal_dcg += ideal_gain / log2((double) (i + 2));
		if (epi->debug_level > 0)
			printf("ndcg2: %ld %ld %3.1f %6.4f %3.1f %6.4f\n", i, cur_level,
					results_gain, results_dcg, ideal_gain, ideal_dcg);
	}
	while (i < res_rels.num_ret) {
		/* Calculate change in results dcg */
		results_gain = get_gain(res_rels.results_rel_list[i], &gains);
		if (results_gain != 0)
			results_dcg += results_gain / log2((double) (i + 2));
		if (epi->debug_level > 0)
			printf("ndcg2: %ld %ld %3.1f %6.4f %3.1f %6.4f\n", i, cur_level,
					results_gain, results_dcg, 0.0, ideal_dcg);
		i++;
	}
	while (ideal_gain > 0.0) {
		/* Calculate change in ideal dcg */
		num_at_level++;
		while (cur_level >= 0
				&& num_at_level > gains.rel_gains[cur_level].num_at_level) {
			num_at_level = 1;
			cur_level--;
			ideal_gain =
					(cur_level >= 0) ? gains.rel_gains[cur_level].gain : 0.0;
		}
		if (ideal_gain > 0.0)
			ideal_dcg += ideal_gain / log2((double) (i + 2));
		if (epi->debug_level > 0)
			printf("ndcg2: %ld %ld %3.1f %6.4f %3.1f %6.4f\n", i, cur_level,
					0.0, results_dcg, ideal_gain, ideal_dcg);
		i++;
	}

	/* Compare sum to ideal NDCG2 */
	if (ideal_dcg > 0.0) {
		eval->values[tm->eval_index].value = results_dcg / ideal_dcg;
	}

	Free(gains.rel_gains);
	return (1);
}

static int setup_gains(const TREC_MEAS *tm, const RES_RELS *res_rels,
		GAINS *gains) {
	FLOAT_PARAM_PAIR *pairs = NULL;
	long num_pairs = 0;
	long i, j;
	long num_gains;

	if (tm->meas_params) {
		pairs = (FLOAT_PARAM_PAIR *) tm->meas_params->param_values;
		num_pairs = tm->meas_params->num_params;
	}

	if (NULL
			== (gains->rel_gains = Malloc(res_rels->num_rel_levels + num_pairs,
					REL_GAIN)))
		return (UNDEF);
	num_gains = 0;
	for (i = 0; i < num_pairs; i++) {
		gains->rel_gains[num_gains].rel_level = atol(pairs[i].name);
		gains->rel_gains[num_gains].gain = (double) pairs[i].value;
		gains->rel_gains[num_gains].num_at_level = 0;
		num_gains++;
	}

	for (i = 0; i < res_rels->num_rel_levels; i++) {
		for (j = 0; j < num_gains && gains->rel_gains[j].rel_level != i; j++)
			;
		if (j < num_gains)
			/* Was included in list of parameters. Update occurrence info */
			gains->rel_gains[j].num_at_level = res_rels->rel_levels[i];
		else {
			/* Not included in list of parameters. New gain level */
			gains->rel_gains[num_gains].rel_level = i;
			gains->rel_gains[num_gains].gain = pow(2.0, (double) i);
			gains->rel_gains[num_gains].num_at_level = res_rels->rel_levels[i];
			num_gains++;
		}
	}

	/* Sort gains by increasing gain value */
	qsort((char *) gains->rel_gains, (int) num_gains, sizeof(REL_GAIN),
			comp_rel_gain);

	gains->total_num_at_levels = 0;
	for (i = 0; i < num_gains; i++)
		gains->total_num_at_levels += gains->rel_gains[i].num_at_level;

	gains->num_gains = num_gains;
	return (1);
}

static int comp_rel_gain(REL_GAIN *ptr1, REL_GAIN *ptr2) {
	return (ptr1->gain - ptr2->gain);
}

static double get_gain(const long rel_level, const GAINS *gains) {
	long i;
	for (i = 0; i < gains->num_gains; i++)
		if (rel_level == gains->rel_gains[i].rel_level)
			return (gains->rel_gains[i].gain);
	return (0.0); /* Print Error ?? */
}