interactions.h

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#pragma once

#include "global_data.h"
#include "interactions_predict.h"

/*
 *  Interactions preprocessing and feature combinations generation
 */

namespace INTERACTIONS
{
/*
 *  Interactions preprocessing
 */

constexpr unsigned char printable_start = ' ';
constexpr unsigned char printable_end = '~';
constexpr unsigned char printable_ns_size = printable_end - printable_start;
constexpr uint64_t valid_ns_size =
    printable_end - printable_start - 1;  // -1 to skip characters ':' and '|' excluded in is_valid_ns()

inline constexpr bool is_printable_namespace(const unsigned char ns)
{
  return ns >= printable_start && ns <= printable_end;
}

// exand all wildcard namespaces in vector<string>
// req_length must be 0 if interactions of any length are allowed, otherwise contains required length
// err_msg will be printed plus exception will be thrown if req_length != 0 and mismatch interaction length.
std::vector<std::string> expand_interactions(
    const std::vector<std::string>& vec, const size_t required_length, const std::string& err_msg);

// remove duplicate interactions and sort namespaces in them (if required)
void sort_and_filter_duplicate_interactions(
    std::vector<std::string>& vec, bool filter_duplicates, size_t& removed_cnt, size_t& sorted_cnt);

/*
 *  Feature combinations generation
 */

// function estimates how many new features will be generated for example and ther sum(value^2).
void eval_count_of_generated_ft(vw& all, example& ec, size_t& new_features_cnt, float& new_features_value);

template <class R, class S, void (*T)(R&, float, S), bool audit, void (*audit_func)(R&, const audit_strings*)>
inline void generate_interactions(vw& all, example_predict& ec, R& dat)
{
  if (all.weights.sparse)
    generate_interactions<R, S, T, audit, audit_func, sparse_parameters>(
        *ec.interactions, all.permutations, ec, dat, all.weights.sparse_weights);
  else
    generate_interactions<R, S, T, audit, audit_func, dense_parameters>(
        *ec.interactions, all.permutations, ec, dat, all.weights.dense_weights);
}

// this code is for C++98/03 complience as I unable to pass null function-pointer as template argument in g++-4.6
template <class R, class S, void (*T)(R&, float, S)>
inline void generate_interactions(vw& all, example_predict& ec, R& dat)
{
  if (all.weights.sparse)
    generate_interactions<R, S, T, sparse_parameters>(
        all.interactions, all.permutations, ec, dat, all.weights.sparse_weights);
  else
    generate_interactions<R, S, T, dense_parameters>(
        all.interactions, all.permutations, ec, dat, all.weights.dense_weights);
}

// C(n,k) = n!/(k!(n-k)!)

inline int64_t choose(int64_t n, int64_t k)
{
  if (k > n)
    return 0;
  if (k < 0)
    return 0;
  if (k == n)
    return 1;
  if (k == 0 && n != 0)
    return 1;
  int64_t r = 1;
  for (int64_t d = 1; d <= k; ++d)
  {
    r *= n--;
    r /= d;
  }
  return r;
}

}  // namespace INTERACTIONS