49 lines
1.7 KiB
C++
49 lines
1.7 KiB
C++
// Copyright 2015-2018 Hans Dembinski
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//
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt
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// or copy at http://www.boost.org/LICENSE_1_0.txt)
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//[ guide_histogram_reduction
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#include <boost/histogram.hpp>
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#include <cassert>
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int main() {
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using namespace boost::histogram;
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// import reduce commands into local namespace to save typing
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using algorithm::rebin;
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using algorithm::shrink;
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using algorithm::slice;
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// make a 2d histogram
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auto h = make_histogram(axis::regular<>(4, 0.0, 4.0), axis::regular<>(4, -2.0, 2.0));
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h(0, -0.9);
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h(1, 0.9);
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h(2, 0.1);
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h(3, 0.1);
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// reduce takes positional commands which are applied to the axes in order
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// - shrink is applied to the first axis; the new axis range is 0.0 to 3.0
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// - rebin is applied to the second axis; pairs of adjacent bins are merged
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auto h2 = algorithm::reduce(h, shrink(0.0, 3.0), rebin(2));
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assert(h2.axis(0) == axis::regular<>(3, 0.0, 3.0));
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assert(h2.axis(1) == axis::regular<>(2, -2.0, 2.0));
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// reduce does not change the total count if the histogram has underflow/overflow bins
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assert(algorithm::sum(h) == 4 && algorithm::sum(h2) == 4);
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// One can also explicitly specify the index of the axis in the histogram on which the
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// command should act, by using this index as the the first parameter. The position of
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// the command in the argument list of reduce is then ignored. We use this to slice only
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// the second axis (axis has index 1 in the histogram) from bin index 2 to 4.
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auto h3 = algorithm::reduce(h, slice(1, 2, 4));
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assert(h3.axis(0) == h.axis(0)); // unchanged
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assert(h3.axis(1) == axis::regular<>(2, 0.0, 2.0));
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}
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//]
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