1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package rand_test
import (
"fmt"
"math/rand"
"os"
"strings"
"text/tabwriter"
)
// These tests serve as an example but also make sure we don't change
// the output of the random number generator when given a fixed seed.
func Example() {
// Seeding with the same value results in the same random sequence each run.
// For different numbers, seed with a different value, such as
// time.Now().UnixNano(), which yields a constantly-changing number.
rand.Seed(42)
answers := []string{
"It is certain",
"It is decidedly so",
"Without a doubt",
"Yes definitely",
"You may rely on it",
"As I see it yes",
"Most likely",
"Outlook good",
"Yes",
"Signs point to yes",
"Reply hazy try again",
"Ask again later",
"Better not tell you now",
"Cannot predict now",
"Concentrate and ask again",
"Don't count on it",
"My reply is no",
"My sources say no",
"Outlook not so good",
"Very doubtful",
}
fmt.Println("Magic 8-Ball says:", answers[rand.Intn(len(answers))])
// Output: Magic 8-Ball says: As I see it yes
}
// This example shows the use of each of the methods on a *Rand.
// The use of the global functions is the same, without the receiver.
func Example_rand() {
// Create and seed the generator.
// Typically a non-fixed seed should be used, such as time.Now().UnixNano().
// Using a fixed seed will produce the same output on every run.
r := rand.New(rand.NewSource(99))
// The tabwriter here helps us generate aligned output.
w := tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', 0)
defer w.Flush()
show := func(name string, v1, v2, v3 interface{}) {
fmt.Fprintf(w, "%s\t%v\t%v\t%v\n", name, v1, v2, v3)
}
// Float32 and Float64 values are in [0, 1).
show("Float32", r.Float32(), r.Float32(), r.Float32())
show("Float64", r.Float64(), r.Float64(), r.Float64())
// ExpFloat64 values have an average of 1 but decay exponentially.
show("ExpFloat64", r.ExpFloat64(), r.ExpFloat64(), r.ExpFloat64())
// NormFloat64 values have an average of 0 and a standard deviation of 1.
show("NormFloat64", r.NormFloat64(), r.NormFloat64(), r.NormFloat64())
// Int31, Int63, and Uint32 generate values of the given width.
// The Int method (not shown) is like either Int31 or Int63
// depending on the size of 'int'.
show("Int31", r.Int31(), r.Int31(), r.Int31())
show("Int63", r.Int63(), r.Int63(), r.Int63())
show("Uint32", r.Uint32(), r.Uint32(), r.Uint32())
// Intn, Int31n, and Int63n limit their output to be < n.
// They do so more carefully than using r.Int()%n.
show("Intn(10)", r.Intn(10), r.Intn(10), r.Intn(10))
show("Int31n(10)", r.Int31n(10), r.Int31n(10), r.Int31n(10))
show("Int63n(10)", r.Int63n(10), r.Int63n(10), r.Int63n(10))
// Perm generates a random permutation of the numbers [0, n).
show("Perm", r.Perm(5), r.Perm(5), r.Perm(5))
// Output:
// Float32 0.2635776 0.6358173 0.6718283
// Float64 0.628605430454327 0.4504798828572669 0.9562755949377957
// ExpFloat64 0.3362240648200941 1.4256072328483647 0.24354758816173044
// NormFloat64 0.17233959114940064 1.577014951434847 0.04259129641113857
// Int31 1501292890 1486668269 182840835
// Int63 3546343826724305832 5724354148158589552 5239846799706671610
// Uint32 2760229429 296659907 1922395059
// Intn(10) 1 2 5
// Int31n(10) 4 7 8
// Int63n(10) 7 6 3
// Perm [1 4 2 3 0] [4 2 1 3 0] [1 2 4 0 3]
}
func ExamplePerm() {
for _, value := range rand.Perm(3) {
fmt.Println(value)
}
// Unordered output: 1
// 2
// 0
}
func ExampleShuffle() {
words := strings.Fields("ink runs from the corners of my mouth")
rand.Shuffle(len(words), func(i, j int) {
words[i], words[j] = words[j], words[i]
})
fmt.Println(words)
// Output:
// [mouth my the of runs corners from ink]
}
func ExampleShuffle_slicesInUnison() {
numbers := []byte("12345")
letters := []byte("ABCDE")
// Shuffle numbers, swapping corresponding entries in letters at the same time.
rand.Shuffle(len(numbers), func(i, j int) {
numbers[i], numbers[j] = numbers[j], numbers[i]
letters[i], letters[j] = letters[j], letters[i]
})
for i := range numbers {
fmt.Printf("%c: %c\n", letters[i], numbers[i])
}
// Output:
// C: 3
// D: 4
// A: 1
// E: 5
// B: 2
}
func ExampleIntn() {
// Seeding with the same value results in the same random sequence each run.
// For different numbers, seed with a different value, such as
// time.Now().UnixNano(), which yields a constantly-changing number.
rand.Seed(86)
fmt.Println(rand.Intn(100))
fmt.Println(rand.Intn(100))
fmt.Println(rand.Intn(100))
// Output:
// 42
// 76
// 30
}
|
