1 // Copyright 2018 Hans Dembinski
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)
7 //[ guide_custom_accumulators
10 #include <boost/format.hpp>
11 #include <boost/histogram.hpp>
12 #include <boost/histogram/accumulators/mean.hpp>
16 using namespace boost::histogram;
17 const auto axis = axis::regular<>(3, 0.0, 1.0);
19 // Create a 1D-profile, which computes the mean of samples in each bin. The
20 // factory function `make_profile` is provided by the library as a shorthand.
21 auto h1 = make_histogram_with(dense_storage<accumulators::mean<>>(), axis);
23 // Argument of `sample` is passed to accumulator.
24 h1(0.0, sample(2)); // sample 2 goes to first bin
25 h1(0.1, sample(2)); // sample 2 goes to first bin
26 h1(0.4, sample(3)); // sample 3 goes to second bin
27 h1(0.5, sample(4)); // sample 4 goes to second bin
29 std::ostringstream os1;
30 for (auto&& x : indexed(h1)) {
31 // Accumulators usually have methods to access their state. Use the arrow
32 // operator to access them. Here, `count()` gives the number of samples,
33 // `value()` the mean, and `variance()` the variance estimate of the mean.
34 os1 << boost::format("%i count %i mean %.1f variance %.1f\n") % x.index() %
35 x->count() % x->value() % x->variance();
37 std::cout << os1.str() << std::flush;
38 assert(os1.str() == "0 count 2 mean 2.0 variance 0.0\n"
39 "1 count 2 mean 3.5 variance 0.5\n"
40 "2 count 0 mean 0.0 variance 0.0\n");
42 // Let's make a custom accumulator, which tracks the maximum of the samples. It must
43 // have a call operator that accepts the argument of the `sample` function. The return
44 // value of the call operator is ignored.
46 void operator()(double x) {
47 if (x > value) value = x;
49 double value = 0; // value is initialized to zero
52 // Create a histogram that uses the custom accumulator.
53 auto h2 = make_histogram_with(dense_storage<max>(), axis);
54 h2(0.0, sample(2)); // sample 2 goes to first bin
55 h2(0.1, sample(2.5)); // sample 2.5 goes to first bin
56 h2(0.4, sample(3)); // sample 3 goes to second bin
57 h2(0.5, sample(4)); // sample 4 goes to second bin
59 std::ostringstream os2;
60 for (auto&& x : indexed(h2)) {
61 os2 << boost::format("%i value %.1f\n") % x.index() % x->value;
63 std::cout << os2.str() << std::flush;
64 assert(os2.str() == "0 value 2.5\n"