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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)
- // clang-format off
- //[ getting_started_listing_01
- #include <algorithm> // std::for_each
- #include <boost/format.hpp> // only needed for printing
- #include <boost/histogram.hpp> // make_histogram, regular, weight, indexed
- #include <cassert> // assert (used to test this example for correctness)
- #include <functional> // std::ref
- #include <iostream> // std::cout, std::flush
- #include <sstream> // std::ostringstream
- int main() {
- using namespace boost::histogram; // strip the boost::histogram prefix
- /*
- Create a 1d-histogram with a regular axis that has 6 equidistant bins on
- the real line from -1.0 to 2.0, and label it as "x". A family of overloaded
- factory functions called `make_histogram` makes creating histograms easy.
- A regular axis is a sequence of semi-open bins. Extra under- and overflow
- bins extend the axis by default (this can be turned off).
- index : -1 | 0 | 1 | 2 | 3 | 4 | 5 | 6
- bin edges: -inf -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 inf
- */
- auto h = make_histogram(axis::regular<>(6, -1.0, 2.0, "x"));
- /*
- Let's fill a histogram with data, typically this happens in a loop.
- STL algorithms are supported. std::for_each is very convenient to fill a
- histogram from an iterator range. Use std::ref in the call, if you don't
- want std::for_each to make a copy of your histogram.
- */
- auto data = {-0.5, 1.1, 0.3, 1.7};
- std::for_each(data.begin(), data.end(), std::ref(h));
- // let's fill some more values manually
- h(-1.5); // is placed in underflow bin -1
- h(-1.0); // is placed in bin 0, bin interval is semi-open
- h(2.0); // is placed in overflow bin 6, bin interval is semi-open
- h(20.0); // is placed in overflow bin 6
- /*
- This does a weighted fill using the `weight` function as an additional
- argument. It may appear at the beginning or end of the argument list. C++
- doesn't have keyword arguments like Python, this is the next-best thing.
- */
- h(0.1, weight(1.0));
- /*
- Iterate over bins with the `indexed` range generator, which provides a
- special accessor object, that can be used to obtain the current bin index,
- and the current bin value by dereferncing (it acts like a pointer to the
- value). Using `indexed` is convenient and gives you better performance than
- looping over the histogram cells with hand-written for loops. By default,
- under- and overflow bins are skipped. Passing `coverage::all` as the
- optional second argument iterates over all bins.
- - Access the value with the dereference operator.
- - Access the current index with `index(d)` method of the accessor.
- - Access the corresponding bin interval view with `bin(d)`.
- The return type of `bin(d)` depends on the axis type (see the axis reference
- for details). It usually is a class that represents a semi-open interval.
- Edges can be accessed with methods `lower()` and `upper()`.
- */
- std::ostringstream os;
- for (auto&& x : indexed(h, coverage::all)) {
- os << boost::format("bin %2i [%4.1f, %4.1f): %i\n")
- % x.index() % x.bin().lower() % x.bin().upper() % *x;
- }
- std::cout << os.str() << std::flush;
- assert(os.str() == "bin -1 [-inf, -1.0): 1\n"
- "bin 0 [-1.0, -0.5): 1\n"
- "bin 1 [-0.5, -0.0): 1\n"
- "bin 2 [-0.0, 0.5): 2\n"
- "bin 3 [ 0.5, 1.0): 0\n"
- "bin 4 [ 1.0, 1.5): 1\n"
- "bin 5 [ 1.5, 2.0): 1\n"
- "bin 6 [ 2.0, inf): 2\n");
- }
- //]
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