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79 lines
2.9 KiB
C++
79 lines
2.9 KiB
C++
//[ getting_started_listing_01
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#include <boost/histogram.hpp>
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#include <iostream>
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int main() {
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namespace bh = boost::histogram;
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using namespace bh::literals; // enables _c suffix
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/*
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create a static 1d-histogram with an axis that has 6 equidistant
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bins on the real line from -1.0 to 2.0, and label it as "x"
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*/
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auto h = bh::make_static_histogram(bh::axis::regular<>(6, -1.0, 2.0, "x"));
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// fill histogram with data, typically this happens in a loop
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// STL algorithms are supported
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auto data = {-0.5, 1.1, 0.3, 1.7};
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h = std::for_each(data.begin(), data.end(), h);
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/*
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a regular axis is a sequence of semi-open bins; extra under- and
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overflow bins extend the axis in the default configuration
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index : -1 0 1 2 3 4 5 6
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bin edge: -inf -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 inf
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*/
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h(-1.5); // put in underflow bin -1
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h(-1.0); // put in bin 0, bin interval is semi-open
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h(2.0); // put in overflow bin 6, bin interval is semi-open
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h(20.0); // put in overflow bin 6
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/*
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do a weighted fill using bh::weight, a wrapper for any type,
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which may appear at the beginning of the argument list
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*/
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h(bh::weight(1.0), 0.1);
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/*
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iterate over bins with a fancy histogram iterator
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- order in which bins are iterated over is an implementation detail
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- iterator dereferences to histogram::element_type, which is defined by
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its storage class; by default something with value() and
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variance() methods; the first returns the
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actual count, the second returns a variance estimate of the count
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(see Rationale section for what this means)
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- idx(N) method returns the index of the N-th axis
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- bin(N_c) method returns current bin of N-th axis; the suffx _c turns
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the argument into a compile-time number, which is needed to return
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different `bin_type`s for different axes
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- `bin_type` usually is a semi-open interval representing the bin, whose
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edges can be accessed with methods `lower()` and `upper()`, but the
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implementation depends on the axis, please look it up in the reference
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*/
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std::cout.setf(std::ios_base::fixed);
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for (auto it = h.begin(); it != h.end(); ++it) {
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const auto bin = it.bin(0_c);
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std::cout << "bin " << it.idx(0) << " x in [" << std::setprecision(1)
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<< std::setw(4) << bin.lower() << ", " << std::setw(4)
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<< bin.upper() << "): " << std::setprecision(1) << it->value()
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<< " +/- " << std::setprecision(3) << std::sqrt(it->variance())
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<< std::endl;
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}
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/* program output: (note that under- and overflow bins appear at the end)
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bin 0 x in [-1.0, -0.5): 1 +/- 1
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bin 1 x in [-0.5, 0.0): 0 +/- 0
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bin 2 x in [ 0.0, 0.5): 1 +/- 1
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bin 3 x in [ 0.5, 1.0): 0 +/- 0
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bin 4 x in [ 1.0, 1.5): 0 +/- 0
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bin 5 x in [ 1.5, 2.0): 0 +/- 0
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bin 6 x in [ 2.0, inf): 2 +/- 1.41421
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bin -1 x in [-inf, -1): 1 +/- 1
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*/
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}
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//]
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