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// Copyright 2015-2018 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_histogram_reduction
#include <boost/histogram.hpp>
#include <cassert>
int main() {
using namespace boost::histogram;
// import reduce commands into local namespace to save typing
using algorithm::rebin;
using algorithm::shrink;
using algorithm::slice;
// make a 2d histogram
auto h = make_histogram(axis::regular<>(4, 0.0, 4.0), axis::regular<>(4, -2.0, 2.0));
h(0, -0.9);
h(1, 0.9);
h(2, 0.1);
h(3, 0.1);
// reduce takes positional commands which are applied to the axes in order
// - shrink is applied to the first axis; the new axis range is 0.0 to 3.0
// - rebin is applied to the second axis; pairs of adjacent bins are merged
auto h2 = algorithm::reduce(h, shrink(0.0, 3.0), rebin(2));
assert(h2.axis(0) == axis::regular<>(3, 0.0, 3.0));
assert(h2.axis(1) == axis::regular<>(2, -2.0, 2.0));
// reduce does not change the total count if the histogram has underflow/overflow bins
assert(algorithm::sum(h) == 4 && algorithm::sum(h2) == 4);
// One can also explicitly specify the index of the axis in the histogram on which the
// command should act, by using this index as the the first parameter. The position of
// the command in the argument list of reduce is then ignored. We use this to slice only
// the second axis (axis has index 1 in the histogram) from bin index 2 to 4.
auto h3 = algorithm::reduce(h, slice(1, 2, 4));
assert(h3.axis(0) == h.axis(0)); // unchanged
assert(h3.axis(1) == axis::regular<>(2, 0.0, 2.0));
}
//]
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