version: 1.10

package rand

import "math/rand"

Overview

Package rand implements pseudo-random number generators.

Random numbers are generated by a Source. Top-level functions, such as Float64
and Int, use a default shared Source that produces a deterministic sequence of
values each time a program is run. Use the Seed function to initialize the
default Source if different behavior is required for each run. The default
Source is safe for concurrent use by multiple goroutines, but Sources created by
NewSource are not.

For random numbers suitable for security-sensitive work, see the crypto/rand
package.

Example:

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))])
// Output: Magic 8-Ball says: As I see it yes

Example:

// 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]

Index

• func ExpFloat64() float64
• func Float32() float32
• func Float64() float64
• func Int() int
• func Int31() int32
• func Int31n(n int32) int32
• func Int63() int64
• func Int63n(n int64) int64
• func Intn(n int) int
• func NormFloat64() float64
• func Perm(n int) []int
• func Read(p []byte) (n int, err error)
• func Seed(seed int64)
• func Shuffle(n int, swap func(i, j int))
• func Uint32() uint32
• func Uint64() uint64
• type Rand
  • func New(src Source) *Rand
  • func (r *Rand) ExpFloat64() float64
  • func (r *Rand) Float32() float32
  • func (r *Rand) Float64() float64
  • func (r *Rand) Int() int
  • func (r *Rand) Int31() int32
  • func (r *Rand) Int31n(n int32) int32
  • func (r *Rand) Int63() int64
  • func (r *Rand) Int63n(n int64) int64
  • func (r *Rand) Intn(n int) int
  • func (r *Rand) NormFloat64() float64
  • func (r *Rand) Perm(n int) []int
  • func (r *Rand) Read(p []byte) (n int, err error)
  • func (r *Rand) Seed(seed int64)
  • func (r *Rand) Shuffle(n int, swap func(i, j int))
  • func (r *Rand) Uint32() uint32
  • func (r *Rand) Uint64() uint64
• type Source
  • func NewSource(seed int64) Source
• type Source64
• type Zipf
  • func NewZipf(r Rand, s float64, v float64, imax uint64) Zipf
  • func (z *Zipf) Uint64() uint64

Examples

• Package
• Perm
• Shuffle
• Shuffle (SlicesInUnison)
• Package (Rand)

Package files

exp.go normal.go rand.go rng.go zipf.go

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.

Example:

for _, value := range rand.Perm(3) {
    fmt.Println(value)
}
// Unordered output: 1
// 2
// 0

func Read
¶

func Read(p []byte) (n int, err error)

Read generates len(p) random bytes from the default Source and writes them into
p. It always returns len(p) and a nil error. Read, unlike the Rand.Read method,
is safe for concurrent use.

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). Seed values that have the same remainder when divided by 2^31-1
generate the same pseudo-random sequence. Seed, unlike the Rand.Seed method, is
safe for concurrent use.

func Shuffle
¶

func Shuffle(n int, swap func(i, j int))

Shuffle pseudo-randomizes the order of elements using the default Source. n is
the number of elements. Shuffle panics if n < 0. swap swaps the elements with
indexes i and j.

Example:

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]

Example:

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 Uint32
¶

func Uint32() uint32

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

func Uint64
¶

func Uint64() uint64

Uint64 returns a pseudo-random 64-bit value as a uint64 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 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). To produce a distribution with a different
rate parameter, callers can adjust the output using:

sample = ExpFloat64() / desiredRateParameter

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

sample = NormFloat64() * desiredStdDev + desiredMean

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) Read
¶

func (r *Rand) Read(p []byte) (n int, err error)

Read generates len(p) random bytes and writes them into p. It always returns
len(p) and a nil error. Read should not be called concurrently with any other
Rand method.

func (*Rand) Seed
¶

func (r *Rand) Seed(seed int64)

Seed uses the provided seed value to initialize the generator to a deterministic
state. Seed should not be called concurrently with any other Rand method.

func (*Rand) Shuffle
¶

func (r *Rand) Shuffle(n int, swap func(i, j int))

Shuffle pseudo-randomizes the order of elements. n is the number of elements.
Shuffle panics if n < 0. swap swaps the elements with indexes i and j.

func (*Rand) Uint32
¶

func (r *Rand) Uint32() uint32

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

func (*Rand) Uint64
¶

func (r *Rand) Uint64() uint64

Uint64 returns a pseudo-random 64-bit value as a uint64.

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. Unlike
the default Source used by top-level functions, this source is not safe for
concurrent use by multiple goroutines.

type Source64
¶

type Source64 interface {
    Source
    Uint64() uint64
}

A Source64 is a Source that can also generate uniformly-distributed
pseudo-random uint64 values in the range [0, 1<<64) directly. If a Rand r’s
underlying Source s implements Source64, then r.Uint64 returns the result of one
call to s.Uint64 instead of making two calls to s.Int63.

type Zipf
¶

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

A Zipf generates Zipf distributed variates.

func NewZipf
¶

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

NewZipf returns a Zipf variate generator. The generator generates values k ∈ [0,
imax] such that P(k) is proportional to (v + k) ** (-s). Requirements: s > 1 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.