histogram.icc

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
*/
 
#include "H5Cpp.h"
#include "HDF5Utils/HistCommon.h"
 
#include <map>
#include <vector>
#include <cassert>
#include <cmath>
#include <cstdint>
#include <numeric>
#include <set>
#include <string>
#include <format>
 
#include <boost/histogram.hpp>
 
 
namespace H5Utils::hist::detail {
 
  // various stuff to inspect the boost histograms
 
  // Concepts to inspect which members the accumulator exposes.
  template <typename T>
  concept HasValue = requires(T t) { t.begin()->value(); };
  template <typename T>
  concept HasVariance = requires(T t) { t.begin()->variance(); };
  template <typename T>
  concept HasCount = requires(T t) { t.begin()->count(); };
  template <typename T>
  concept HasSumOfWeights = requires(T t) { t.begin()->sum_of_weights(); };
  template <typename T>
  concept HasSumOfWeightsSquared = requires(T t) {
    t.begin()->sum_of_weights_squared();
  };
 
  // figure out the output array type
  template <typename T>
  struct array_type
  {
    using type = typename T::value_type;
  };
  // this needs further specialization in some cases
  template <typename T>
  using iter_value_t = decltype(
    std::declval<T>().begin()->value());
  template <HasValue T>
  struct array_type<T>
  {
    using type = std::remove_cv_t<std::remove_reference_t<iter_value_t<T>>>;
  };
  template <typename T>
  using array_t = typename array_type<T>::type;
 
 
  // function to flatten the histogram array
  template <typename T, typename F>
  std::vector<array_t<T>> get_flat_hist_array(const T& hist,
                                              const F& value_getter)
  {
    using out_t = std::vector<array_t<T>>;
    namespace bh = boost::histogram;
 
    // calculate a global index for the flat output array
    auto global_index = [&hist](const auto& hist_idx)
    {
      // This is unrolling the index to a c-style array. We calculate
      // a global index, starting with the last dimension. The last
      // dimension is just added to the global index. Each previous
      // dimension needs to multiply the index by the cumulative
      // product of the maximum index of subsequent dimensions.
      size_t global = 0;
      size_t stride = 1;
      for (size_t dim_p1 = hist.rank(); dim_p1 != 0; dim_p1--) {
        size_t dim = dim_p1 - 1;
        auto ops = hist.axis(dim).options();
        int underflow = (ops & bh::axis::option::underflow) ? 1 : 0;
        int overflow = (ops & bh::axis::option::overflow) ? 1 : 0;
        // ugly check to decide if we have to add underflow offset
        int h5idx_signed = hist_idx.index(dim) + underflow;
        if (h5idx_signed < 0) throw std::logic_error("neg signed index");
        size_t h5idx = static_cast<size_t>(h5idx_signed);
        global += h5idx * stride;
        stride *= hist.axis(dim).size() + underflow + overflow;
      }
      return global;
    };
 
    out_t out(hist.size());
    std::set<size_t> used_indices;
    for (const auto& x : bh::indexed(hist, bh::coverage::all)) {
      size_t global = global_index(x);
      if (!used_indices.insert(global).second) {
        throw std::logic_error(
          "repeat global index: " + std::to_string(global));
      }
      out.at(global) = value_getter(x);
    }
    return out;
  }
 
 
  // Axes inspection
 
  // Runtime functions to check axes, this information can't always be
  // determined statically with the public api.
  //
  // Returns true when all bin widths are equal and positive (regular
  // axis).
  inline bool is_regular_axis(const std::vector<double>& edges) {
    if (edges.size() < 2) return false;
    const double width0 = edges[1] - edges[0];
    if (width0 <= 0.0) return false;
    for (size_t i = 2; i < edges.size(); i++) {
      const double width = edges[i] - edges[i-1];
      if (std::abs(width - width0) > 1e-5 * std::abs(width0)) { return false; }
    }
    return true;
  }
 
  // Returns true if bins are contiguous integer sequence
  inline bool is_contiguous(const std::vector<int64_t>& vals) {
    if (vals.size() < 2) return true;
    for (size_t i = 1; i < vals.size(); ++i) {
      if (vals[i] != vals[i-1] + 1) return false;
    }
    return true;
  }
 
  // Helper: construct an Axis with name/underflow/overflow filled from the
  // boost axis options.  Each overload then only needs to set ax.edges.
  inline Axis make_axis(const auto& bh_ax, const std::string& name)
  {
    namespace opts = boost::histogram::axis::option;
    Axis ax;
    ax.name      = name;
    ax.underflow = (bh_ax.options() & opts::underflow) ? true : false;
    ax.overflow  = (bh_ax.options() & opts::overflow)  ? true : false;
    return ax;
  }
 
 
  // Concepts to label descrete axes
 
  // A random-access sequence of string labels.
  // Matches std::vector<string>, std::deque<string>, etc.
  template<typename L>
  concept LabelList = requires(const L& lst, size_t i) {
    { lst[i] } -> std::convertible_to<std::string>;
    { lst.size() } -> std::convertible_to<size_t>;
  };
 
  // A map-like container with key_type and at(key) -> string.
  // Matches std::map<K, string> but not std::vector<string>.
  template<typename M>
  concept LabelMap = requires(const M& m) {
    { m.at(std::declval<typename M::key_type>()) }
        -> std::convertible_to<std::string>;
    { m.size() } -> std::convertible_to<size_t>;
  };
 
  // Either a positional label list or a keyed label map.
  template<typename T>
  concept LabelOverride = LabelList<T> || LabelMap<T>;
 
  // Positional list of per-axis label overrides.
  // Supports std::vector, std::deque (operator[] + size() on const ref).
  template<typename L>
  concept AxisOverrideSeq = requires(const L& l, size_t i) {
    l[i];
    { l.size() } -> std::convertible_to<size_t>;
  };
 
  // String-keyed map of per-axis label overrides.
  // at(axis_name) returns the label info; find/end used for existence
  // check.
  template<typename M>
  concept AxisOverrideMap = requires(const M& m) {
    m.at(std::declval<const std::string&>());
    m.find(std::declval<const std::string&>()) != m.end();
  };
 
  // General axis override match
  template <typename Labels>
  concept AxisOverrides = AxisOverrideSeq<Labels> || AxisOverrideMap<Labels>;
 
  // Axis whose bins expose lower()/upper() (regular, variable).
  // Discrete axes (integer, category) iterate to raw values — no lower().
  template<typename Ax>
  concept ContinuousAxis = requires(const Ax& ax) {
    { ax.begin()->lower() } -> std::convertible_to<double>;
  };
 
  // Concept: axis with no lower()/upper() per bin (category, integer).
  template<typename Ax>
  concept DiscreteAxis = !ContinuousAxis<Ax>;
 
 
  // Axis reading functions
  //
  // There are several overloads to provide maximum flexibility, both
  // in what axes are used from boost::histogram and how the user
  // decides to provide labels for the discrete axis cases.
 
  // discrete axis where the user has provided labels for each value
  template<LabelList List>
  Axis read_one_axis(const DiscreteAxis auto& bh_ax,
                     const std::pair<std::string, List>& meta)
  {
    auto ax = make_axis(bh_ax, meta.first);
 
    const auto& labels = meta.second;
    if (labels.size() != static_cast<size_t>(bh_ax.size())) {
      throw std::invalid_argument(
        std::format(
          "axis '{}': label count ({}) != bin count ({})",
          ax.name, labels.size(), bh_ax.size() ));
    }
 
    std::vector<std::string> edge_labels;
    edge_labels.reserve(labels.size());
    for (size_t i = 0; i < labels.size(); ++i)
      edge_labels.push_back(labels[i]);
    ax.edges = std::move(edge_labels);
    return ax;
  }
 
  // Map-based labeled categorical overload: key = category value,
  // value = label.
  //
  // Reorders map entries to axis bin order, then delegates to
  // LabelList overload.
  template<LabelMap Map>
  Axis read_one_axis(const DiscreteAxis auto& bh_ax,
                     const std::pair<std::string, Map>& meta)
  {
    std::vector<std::string> ordered_labels;
    for (const auto& bin : bh_ax) {
      ordered_labels.push_back(meta.second.at(bin));
    }
    return read_one_axis(bh_ax,
      std::pair<std::string, std::vector<std::string>>{
          meta.first, std::move(ordered_labels)});
  }
 
  // Continuous-axis overload (regular, variable): bins are interval_view.
  Axis read_one_axis(const ContinuousAxis auto& bh_ax,
                     const std::string& meta)
  {
    auto ax = make_axis(bh_ax, meta);
 
    std::vector<double> dedges;
    for (const auto& bin : bh_ax) dedges.push_back(bin.lower());
    if (bh_ax.size() > 0) dedges.push_back(bh_ax.rbegin()->upper());
    if (is_regular_axis(dedges)) {
      ax.edges = regular_axis_t{
        dedges.front(), dedges.back(), dedges.size() - 1};
    } else {
      ax.edges = std::move(dedges);
    }
    return ax;
  }
 
  // Continuous axes reject non-empty label overrides; name taken from
  // meta.first.
  template<LabelOverride Override>
  Axis read_one_axis(const ContinuousAxis auto& bh_ax,
                     const std::pair<std::string, Override>& meta)
  {
    if (meta.second.size() > 0) {
      throw std::invalid_argument(std::format(
        "axis '{}' is continuous (regular/variable): "
        "{} label(s) provided but labels are not valid "
        "for this axis type",
        meta.first, meta.second.size()));
    }
    return read_one_axis(bh_ax, meta.first);
  }
 
  // Discrete-axis overload (integer, category): bins are raw values
  // -> int64_t.
  Axis read_one_axis(const auto& bh_ax, const std::string& meta)
  {
    auto ax = make_axis(bh_ax, meta);
 
    std::vector<int64_t> int_vals;
    for (const auto& bin : bh_ax) int_vals.push_back(static_cast<int64_t>(bin));
    if (is_contiguous(int_vals)) {
      ax.edges = std::pair<int64_t,int64_t>{int_vals.front(), int_vals.back()};
    } else {
      ax.edges = std::move(int_vals);
    }
    return ax;
  }
 
  // Extract axis name from plain-string or pair<string,T> metadata.
  inline const std::string& get_axis_name(const std::string& m) {
    return m;
  }
  template<typename T>
  inline const std::string& get_axis_name(
      const std::pair<std::string, T>& m) {
    return m.first;
  }
 
 
  // Top-level Axis builder functions
 
  // Basic case with no labeling overrides. Labels provided via via
  // per-axis metadata.
  template <typename T>
  std::vector<Axis> get_axes(const T& hist) {
    std::vector<Axis> axes;
    hist.for_each_axis([&axes](const auto& bh_ax) {
      axes.push_back(read_one_axis(bh_ax, bh_ax.metadata()));
    });
    return axes;
  }
 
  // Positional-list override: labels[i] is the LabelList or LabelMap
  // for axis i.
  template<typename Hist, AxisOverrideSeq Labels>
  std::vector<Axis> get_axes(const Hist& hist, const Labels& labels)
  {
    if (labels.size() != hist.rank()) {
      throw std::invalid_argument(std::format(
        "label list has {} entries but histogram has {} axes",
        labels.size(), hist.rank()));
    }
    std::vector<Axis> axes;
    size_t i = 0;
    hist.for_each_axis([&](const auto& bh_ax) {
      const auto& lbl = labels[i++];
      using lbl_t = std::decay_t<decltype(lbl)>;
      axes.push_back(read_one_axis(
        bh_ax,
        std::pair<std::string, lbl_t>{
          get_axis_name(bh_ax.metadata()), lbl}));
    });
    return axes;
  }
 
  // Map-based override: axes absent from the map fall back to metadata.
  template<typename Hist, AxisOverrideMap Labels>
  std::vector<Axis> get_axes(const Hist& hist, const Labels& labels)
  {
    std::vector<Axis> axes;
    hist.for_each_axis([&](const auto& bh_ax) {
      const std::string& name = get_axis_name(bh_ax.metadata());
      auto it = labels.find(name);
      if (it != labels.end()) {
        if constexpr (ContinuousAxis<std::decay_t<decltype(bh_ax)>>) {
          throw std::invalid_argument(std::format(
            "axis '{}' is continuous (regular/variable) and cannot "
            "have string labels; remove it from the label map",
            name));
        }
        const auto& lbl = it->second;
        using lbl_t = std::decay_t<decltype(lbl)>;
        axes.push_back(read_one_axis(
          bh_ax,
          std::pair<std::string, lbl_t>{name, lbl}));
      } else {
        axes.push_back(read_one_axis(bh_ax, bh_ax.metadata()));
      }
    });
    return axes;
  }
 
 
  // Main histogram storage writing functions
 
  // Simple utility to calculate integer products
  template <typename T>
  auto product(const std::vector<T>& v) {
    return std::accumulate(
      v.begin(), v.end(), T(1), std::multiplies<hsize_t>{});
  }
 
  // Return the UHI storage type string for histogram type T.
  template <typename T>
  std::string storage_type_name() {
    if constexpr (HasSumOfWeightsSquared<T>) {
      return "weighted_mean";
    } else if constexpr (HasCount<T>) {
      return "mean";
    } else if constexpr (HasVariance<T>) {
      return "weighted";
    } else if constexpr (std::is_integral_v<array_t<T>>) {
      return "int";
    } else {
      return "double";
    }
  }
 
  // internal top level histogram writer
  template <typename T>
  void write_hist_impl(
    H5::Group& parent_group,
    const T& hist,
    const std::string& name,
    const std::vector<Axis>& axes)
  {
    // build the data space
    std::vector<hsize_t> ds_dims;
    for (const auto& axis: axes) {
      size_t total_size =
        std::visit([](const auto& e) { return n_bins(e); }, axis.edges)
        + (axis.underflow ? 1u : 0u)
        + (axis.overflow  ? 1u : 0u);
      ds_dims.push_back(static_cast<hsize_t>(total_size));
    }
    H5::DataSpace space(ds_dims.size(), ds_dims.data());
 
    // Create histogram group and write UHI schema version
    H5::Group group = parent_group.createGroup(name);
    write_int_attr(group, "uhi_schema", 1);
    group.createGroup("metadata");
    group.createGroup("writer_info");
 
    // Dataset creation properties for storage datasets
    H5::DSetCreatPropList props;
    props.setChunk(ds_dims.size(), ds_dims.data());
    props.setDeflate(7);
    chkerr(
      H5Pset_dset_no_attrs_hint(props.getId(), true),
      "no attribute hint");
    H5::DataType type = hdf5_t<array_t<T>>;
 
    // Write ref_axes
    write_axes(group, axes);
 
    // Write storage group
    H5::Group storage = group.createGroup("storage");
    write_str_attr(storage, "type", storage_type_name<T>());
 
    // Helper to write a named dataset into the storage group
    auto add_dataset = [&hist, &type, &space, &props, &storage](
      const std::string& ds_name,
      const auto& func) {
      auto flat = get_flat_hist_array<T>(hist, func);
      assert(
        space.getSelectNpoints() == static_cast<hssize_t>(flat.size()));
      storage.createDataSet(ds_name, type, space, props)
             .write(flat.data(), type);
    };
 
    // values (the primary bin contents)
    if constexpr (HasValue<T>) {
      add_dataset("values",
        [](const auto& x) { return x->value(); });
    } else {
      add_dataset("values",
        [](const auto& x) { return *x; });
    }
    // variances
    if constexpr (HasVariance<T>) {
      add_dataset("variances",
        [](const auto& x) { return x->variance(); });
    }
    // count (mean / weighted_mean accumulators)
    if constexpr (HasCount<T>) {
      add_dataset("count",
        [](const auto& x) { return x->count(); });
    }
    // sum_of_weights (weighted_mean accumulator)
    if constexpr (HasSumOfWeights<T>) {
      add_dataset("sum_of_weights",
        [](const auto& x) { return x->sum_of_weights(); });
    }
    // sum_of_weights_squared (weighted_mean accumulator)
    if constexpr (HasSumOfWeightsSquared<T>) {
      add_dataset("sum_of_weights_squared",
        [](const auto& x) { return x->sum_of_weights_squared(); });
    }
  }
}
 
namespace H5Utils::hist {
 
  // main hist writing function, this should be all anyone needs to
  // call
  template <typename T>
  void write_hist_to_group(
    H5::Group& parent_group,
    const T& hist,
    const std::string& name)
  {
    detail::write_hist_impl(
      parent_group, hist, name, detail::get_axes(hist));
  }
 
  // Overload with external label override (positional list or name map).
  template <typename T, detail::AxisOverrides Labels>
  void write_hist_to_group(
    H5::Group& parent_group,
    const T& hist,
    const std::string& name,
    const Labels& labels)
  {
    detail::write_hist_impl(
      parent_group, hist, name, detail::get_axes(hist, labels));
  }
}