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// Copyright 2018 Hans Dembinski
//
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt
// or copy at http://www.boost.org/LICENSE_1_0.txt)
//[ guide_stdlib_algorithms
#include <boost/histogram.hpp>
#include <cassert>
#include <algorithm> // fill, any_of, min_element, max_element
#include <cmath> // sqrt
#include <numeric> // partial_sum, inner_product
int main() {
using namespace boost::histogram;
// make histogram that represents a probability density function (PDF)
auto h1 = make_histogram(axis::regular<>(4, 1.0, 3.0));
// make indexed range to skip underflow and overflow cells
auto ind = indexed(h1);
// use std::fill to set all counters to 0.25 (except under- and overflow counters)
std::fill(ind.begin(), ind.end(), 0.25);
// compute the cumulative density function (CDF), overriding cell values
std::partial_sum(ind.begin(), ind.end(), ind.begin());
assert(h1.at(-1) == 0.00);
assert(h1.at(0) == 0.25);
assert(h1.at(1) == 0.50);
assert(h1.at(2) == 0.75);
assert(h1.at(3) == 1.00);
assert(h1.at(4) == 0.00);
// use any_of to check if any cell values are smaller than 0.1,
auto b = std::any_of(ind.begin(), ind.end(), [](const auto& x) { return x < 0.1; });
assert(b == false); // under- and overflow cells are zero, but skipped
// find minimum element
auto min_it = std::min_element(ind.begin(), ind.end());
assert(*min_it == 0.25); // under- and overflow cells are skipped
// find maximum element
auto max_it = std::max_element(ind.begin(), ind.end());
assert(*max_it == 1.0);
// make second PDF
auto h2 = make_histogram(axis::regular<>(4, 1.0, 4.0));
h2.at(0) = 0.1;
h2.at(1) = 0.3;
h2.at(2) = 0.2;
h2.at(3) = 0.4;
// computing cosine similiarity: cos(theta) = A dot B / sqrt((A dot A) * (B dot B))
auto ind2 = indexed(h2);
const auto aa = std::inner_product(ind.begin(), ind.end(), ind.begin(), 0.0);
const auto bb = std::inner_product(ind2.begin(), ind2.end(), ind2.begin(), 0.0);
const auto ab = std::inner_product(ind.begin(), ind.end(), ind2.begin(), 0.0);
const auto cos_sim = ab / std::sqrt(aa * bb);
assert(std::abs(cos_sim - 0.967) < 1e-2);
}
//]
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