github.com/gopherd/gonum@v0.0.4/stat/sampleuv/withoutreplacement_test.go (about)

     1  // Copyright ©2017 The Gonum Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package sampleuv
     6  
     7  import (
     8  	"testing"
     9  
    10  	"math/rand"
    11  
    12  	"github.com/gopherd/gonum/floats"
    13  )
    14  
    15  func TestWithoutReplacement(t *testing.T) {
    16  	for cas, test := range []struct {
    17  		N      int
    18  		K      int
    19  		Src    *rand.Rand
    20  		Trials int
    21  		Tol    float64
    22  	}{
    23  		{
    24  			// Test with perm and source.
    25  			N: 10, K: 5, Src: rand.New(rand.NewSource(1)),
    26  			Trials: 100000, Tol: 1e-3,
    27  		},
    28  		{
    29  			// Test without perm and with source.
    30  			N: 10, K: 3, Src: rand.New(rand.NewSource(1)),
    31  			Trials: 100000, Tol: 1e-3,
    32  		},
    33  	} {
    34  		dist := make([]float64, test.N)
    35  		for trial := 0; trial < test.Trials; trial++ {
    36  			idxs := make([]int, test.K)
    37  			WithoutReplacement(idxs, test.N, test.Src)
    38  
    39  			allDiff := true
    40  			for i := 0; i < len(idxs); i++ {
    41  				v := idxs[i]
    42  				for j := i + 1; j < len(idxs); j++ {
    43  					if v == idxs[j] {
    44  						allDiff = false
    45  						break
    46  					}
    47  				}
    48  			}
    49  			if !allDiff {
    50  				t.Errorf("Cas %d: Repeat in sampling. Idxs =%v", cas, idxs)
    51  			}
    52  			for _, v := range idxs {
    53  				dist[v]++
    54  			}
    55  		}
    56  		div := 1 / (float64(test.Trials) * float64(test.K))
    57  		floats.Scale(div, dist)
    58  		want := make([]float64, test.N)
    59  		for i := range want {
    60  			want[i] = 1 / float64(test.N)
    61  		}
    62  		if !floats.EqualApprox(want, dist, test.Tol) {
    63  			t.Errorf("Cas %d: biased sampling. Want = %v, got = %v", cas, want, dist)
    64  		}
    65  	}
    66  }