std::fisher_f_distribution

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <random>
#include <vector>
 
template<int Height = 5, int BarWidth = 1, int Padding = 1, int Offset = 0, class Seq>
void draw_vbars(Seq&& s, const bool DrawMinMax = true)
{
 static_assert(0 < Height and 0 < BarWidth and 0 <= Padding and 0 <= Offset);
 
 auto cout_n = [](auto&& v, int n = 1)
 {
 while (n-- > 0)
 std::cout << v;
 };
 
 const auto [min, max] = std::minmax_element (std::cbegin (s), std::cend (s));
 
 std::vector <std::div_t > qr;
 for (typedef decltype(*std::cbegin (s)) V; V e : s)
 qr.push_back(std::div (std::lerp (V(0), 8 * Height,
 (e - *min) / (*max - *min)), 8));
 
 for (auto h{Height}; h-- > 0; cout_n('\n'))
 {
 cout_n(' ', Offset);
 
 for (auto dv : qr)
 {
 const auto q{dv.quot}, r{dv.rem};
 unsigned char d[]{0xe2, 0x96, 0x88, 0}; // Full Block: '█'
 q < h ? d[0] = ' ', d[1] = 0 : q == h ? d[2] -= (7 - r) : 0;
 cout_n(d, BarWidth), cout_n(' ', Padding);
 }
 
 if (DrawMinMax && Height > 1)
 Height - 1 == h ? std::cout << "┬ " << *max:
 h ? std::cout << "│ "
 : std::cout << "┴ " << *min;
 }
}
 
int main()
{
 std::random_device rd{};
 std::mt19937 gen{rd()};
 
 auto fisher = [&gen](const float d1, const float d2)
 {
 std::fisher_f_distribution<float> d{d1 /* m */, d2 /* n */};
 
 const int norm = 1'00'00;
 const float cutoff = 0.002f;
 
 std::map <int, int> hist{};
 for (int n = 0; n != norm; ++n)
 ++hist[std::round (d(gen))];
 
 std::vector <float> bars;
 std::vector <int> indices;
 for (auto const& [n, p] : hist)
 if (float x = p * (1.0 / norm); cutoff < x)
 {
 bars.push_back(x);
 indices.push_back(n);
 }
 
 std::cout << "d1 = " << d1 << ", d2 = " << d2 << ":\n";
 for (draw_vbars<4, 3>(bars); int n : indices)
 std::cout << std::setw (2) << n << " ";
 std::cout << "\n\n";
 };
 
 fisher(/* d1 = */ 1.0f, /* d2 = */ 5.0f);
 fisher(/* d1 = */ 15.0f, /* d2 = */ 10.f);
 fisher(/* d1 = */ 100.0f, /* d2 = */ 3.0f);
}

d1 = 1, d2 = 5:
███ ┬ 0.4956
███ │
███ ▇▇▇ │
███ ███ ▇▇▇ ▄▄▄ ▂▂▂ ▂▂▂ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ┴ 0.0021
 0 1 2 3 4 5 6 7 8 9 10 11 12 14
 
d1 = 15, d2 = 10:
 ███ ┬ 0.6252
 ███ │
 ███ ▂▂▂ │
▆▆▆ ███ ███ ▃▃▃ ▁▁▁ ▁▁▁ ▁▁▁ ┴ 0.0023
 0 1 2 3 4 5 6
 
d1 = 100, d2 = 3:
 ███ ┬ 0.4589
 ███ │
▁▁▁ ███ ▅▅▅ │
███ ███ ███ ▆▆▆ ▃▃▃ ▂▂▂ ▂▂▂ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ▁▁▁ ┴ 0.0021
 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16