...

Package rand

import "math/rand"
概览
索引
示例

概览 ▾

rand 包实现了伪随机数生成器.

随机数由一个 Source 生成。像 Float64 和 Int 这样的顶级函数使用默认共享的 Source, 它会在每次程序运行时产生一系列确定的值。若每次运行都需要不同的行为,需使用 Seed 函数来初始化默认的 Source。对于多Go程并发来说,默认的 Source 是安全的。

示例

代码:

rand.Seed(42) // Try changing this number!
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))])

输出:

Magic 8-Ball says: As I see it yes

示例 (Rand)

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.

代码:

// 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))

输出:

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 ExpFloat64

func ExpFloat64() float64

ExpFloat64 returns an exponentially distributed float64 in the range (0, +math.MaxFloat64] with an exponential distribution whose rate parameter (lambda) is 1 and whose mean is 1/lambda (1) from the default Source. To produce a distribution with a different rate parameter, callers can adjust the output using:

sample = ExpFloat64() / desiredRateParameter

func Float32

func Float32() float32

Float32 returns, as a float32, a pseudo-random number in [0.0,1.0) from the default Source.

func Float64

func Float64() float64

Float64 returns, as a float64, a pseudo-random number in [0.0,1.0) from the default Source.

func Int

func Int() int

Int returns a non-negative pseudo-random int from the default Source.

func Int31

func Int31() int32

Int31 returns a non-negative pseudo-random 31-bit integer as an int32 from the default Source.

func Int31n

func Int31n(n int32) int32

Int31n returns, as an int32, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.

func Int63

func Int63() int64

Int63 returns a non-negative pseudo-random 63-bit integer as an int64 from the default Source.

func Int63n

func Int63n(n int64) int64

Int63n returns, as an int64, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.

func Intn

func Intn(n int) int

Intn returns, as an int, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.

func NormFloat64

func NormFloat64() float64

NormFloat64 returns a normally distributed float64 in the range [-math.MaxFloat64, +math.MaxFloat64] with standard normal distribution (mean = 0, stddev = 1) from the default Source. To produce a different normal distribution, callers can adjust the output using:

sample = NormFloat64() * desiredStdDev + desiredMean

func Perm

func Perm(n int) []int

Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n) from the default Source.

func Seed

func Seed(seed int64)

Seed uses the provided seed value to initialize the default Source to a deterministic state. If Seed is not called, the generator behaves as if seeded by Seed(1).

func Uint32

func Uint32() uint32

Uint32 returns a pseudo-random 32-bit value as a uint32 from the default Source.

type Rand

type Rand struct {
    // contains filtered or unexported fields
}

A Rand is a source of random numbers.

func New

func New(src Source) *Rand

New returns a new Rand that uses random values from src to generate other random values.

func (*Rand) ExpFloat64

func (r *Rand) ExpFloat64() float64

ExpFloat64 按照率参数(lambda)为 1,均值为 1/lambda (1) 来返回一个在区间 (0, +math.MaxFloat64] 内程指数分布的 float64。要以不同的率参数产生一个分布, 调用者只需通过:

范例 = ExpFloat64() / 所需的率参数

来调整输出即可。

func (*Rand) Float32

func (r *Rand) Float32() float32

Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).

func (*Rand) Float64

func (r *Rand) Float64() float64

Float64 returns, as a float64, a pseudo-random number in [0.0,1.0).

func (*Rand) Int

func (r *Rand) Int() int

Int returns a non-negative pseudo-random int.

func (*Rand) Int31

func (r *Rand) Int31() int32

Int31 returns a non-negative pseudo-random 31-bit integer as an int32.

func (*Rand) Int31n

func (r *Rand) Int31n(n int32) int32

Int31n returns, as an int32, a non-negative pseudo-random number in [0,n). It panics if n <= 0.

func (*Rand) Int63

func (r *Rand) Int63() int64

Int63 returns a non-negative pseudo-random 63-bit integer as an int64.

func (*Rand) Int63n

func (r *Rand) Int63n(n int64) int64

Int63n returns, as an int64, a non-negative pseudo-random number in [0,n). It panics if n <= 0.

func (*Rand) Intn

func (r *Rand) Intn(n int) int

Intn returns, as an int, a non-negative pseudo-random number in [0,n). It panics if n <= 0.

func (*Rand) NormFloat64

func (r *Rand) NormFloat64() float64

NormFloat64 按照标准正态分布(均值 = 0,标准差 = 1)来返回一个在区间 (0, +math.MaxFloat64] 内程正态分布的 float64。要产生一个不同的正态分布, 调用者只需通过:

范例 = NormFloat64() * 所需的标准差 + 所需的均值

来调整输出即可。

func (*Rand) Perm

func (r *Rand) Perm(n int) []int

Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).

func (*Rand) Seed

func (r *Rand) Seed(seed int64)

Seed uses the provided seed value to initialize the generator to a deterministic state.

func (*Rand) Uint32

func (r *Rand) Uint32() uint32

Uint32 returns a pseudo-random 32-bit value as a uint32.

type Source

type Source interface {
    Int63() int64
    Seed(seed int64)
}

A Source represents a source of uniformly-distributed pseudo-random int64 values in the range [0, 1<<63).

func NewSource

func NewSource(seed int64) Source

NewSource returns a new pseudo-random Source seeded with the given value.

type Zipf

type Zipf struct {
    // contains filtered or unexported fields
}

Zipf 生成齐夫分布变量。

func NewZipf

func NewZipf(r *Rand, s float64, v float64, imax uint64) *Zipf

NewZipf returns a Zipf generating variates p(k) on [0, imax] proportional to (v+k)**(-s) where s>1 and k>=0, and v>=1.

func (*Zipf) Uint64

func (z *Zipf) Uint64() uint64

Uint64 returns a value drawn from the Zipf distribution described by the Zipf object.