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_projection
8
9 #include <boost/histogram.hpp>
10 #include <cassert>
11 #include <iostream>
12 #include <sstream>
13
main()14 int main() {
15 using namespace boost::histogram;
16 using namespace literals; // enables _c suffix
17
18 // make a 2d histogram
19 auto h = make_histogram(axis::regular<>(3, -1.0, 1.0), axis::integer<>(0, 2));
20
21 h(-0.9, 0);
22 h(0.9, 1);
23 h(0.1, 0);
24
25 auto hr0 = algorithm::project(h, 0_c); // keep only first axis
26 auto hr1 = algorithm::project(h, 1_c); // keep only second axis
27
28 // reduce does not remove counts; returned histograms are summed over
29 // the removed axes, so h, hr0, and hr1 have same number of total counts;
30 // we compute the sum of counts with the sum algorithm
31 assert(algorithm::sum(h) == 3 && algorithm::sum(hr0) == 3 && algorithm::sum(hr1) == 3);
32
33 std::ostringstream os1;
34 for (auto&& x : indexed(h))
35 os1 << "(" << x.index(0) << ", " << x.index(1) << "): " << *x << "\n";
36 std::cout << os1.str() << std::flush;
37 assert(os1.str() == "(0, 0): 1\n"
38 "(1, 0): 1\n"
39 "(2, 0): 0\n"
40 "(0, 1): 0\n"
41 "(1, 1): 0\n"
42 "(2, 1): 1\n");
43
44 std::ostringstream os2;
45 for (auto&& x : indexed(hr0)) os2 << "(" << x.index(0) << ", -): " << *x << "\n";
46 std::cout << os2.str() << std::flush;
47 assert(os2.str() == "(0, -): 1\n"
48 "(1, -): 1\n"
49 "(2, -): 1\n");
50
51 std::ostringstream os3;
52 for (auto&& x : indexed(hr1)) os3 << "(- ," << x.index(0) << "): " << *x << "\n";
53 std::cout << os3.str() << std::flush;
54 assert(os3.str() == "(- ,0): 2\n"
55 "(- ,1): 1\n");
56 }
57
58 //]
59