1 // Copyright 2015-2018 Hans Dembinski
2 //
3 // Distributed under the Boost Software License, Version 1.0.
4 // (See accompanying file LICENSE_1_0.txt
5 // or copy at http://www.boost.org/LICENSE_1_0.txt)
6
7 //[ guide_histogram_reduction
8
9 #include <boost/histogram.hpp>
10 #include <cassert>
11
main()12 int main() {
13 using namespace boost::histogram;
14 // import reduce commands into local namespace to save typing
15 using algorithm::rebin;
16 using algorithm::shrink;
17 using algorithm::slice;
18
19 // make a 2d histogram
20 auto h = make_histogram(axis::regular<>(4, 0.0, 4.0), axis::regular<>(4, -2.0, 2.0));
21
22 h(0, -0.9);
23 h(1, 0.9);
24 h(2, 0.1);
25 h(3, 0.1);
26
27 // reduce takes positional commands which are applied to the axes in order
28 // - shrink is applied to the first axis; the new axis range is 0.0 to 3.0
29 // - rebin is applied to the second axis; pairs of adjacent bins are merged
30 auto h2 = algorithm::reduce(h, shrink(0.0, 3.0), rebin(2));
31
32 assert(h2.axis(0) == axis::regular<>(3, 0.0, 3.0));
33 assert(h2.axis(1) == axis::regular<>(2, -2.0, 2.0));
34
35 // reduce does not change the total count if the histogram has underflow/overflow bins
36 assert(algorithm::sum(h) == 4 && algorithm::sum(h2) == 4);
37
38 // One can also explicitly specify the index of the axis in the histogram on which the
39 // command should act, by using this index as the the first parameter. The position of
40 // the command in the argument list of reduce is then ignored. We use this to slice only
41 // the second axis (axis has index 1 in the histogram) from bin index 2 to 4.
42 auto h3 = algorithm::reduce(h, slice(1, 2, 4));
43
44 assert(h3.axis(0) == h.axis(0)); // unchanged
45 assert(h3.axis(1) == axis::regular<>(2, 0.0, 2.0));
46 }
47
48 //]
49