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:


Example:

  1. // Create and seed the generator.
  2. // Typically a non-fixed seed should be used, such as time.Now().UnixNano().
  3. // Using a fixed seed will produce the same output on every run.
  4. r := rand.New(rand.NewSource(99))
  6. // The tabwriter here helps us generate aligned output.
  7. w := tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', 0)
  8. defer w.Flush()
  9. show := func(name string, v1, v2, v3 interface{}) {
  10.     fmt.Fprintf(w, "%s\t%v\t%v\t%v\n", name, v1, v2, v3)
  11. }
  13. // Float32 and Float64 values are in [0, 1).
  14. show("Float32", r.Float32(), r.Float32(), r.Float32())
  15. show("Float64", r.Float64(), r.Float64(), r.Float64())
  17. // ExpFloat64 values have an average of 1 but decay exponentially.
  18. show("ExpFloat64", r.ExpFloat64(), r.ExpFloat64(), r.ExpFloat64())
  20. // NormFloat64 values have an average of 0 and a standard deviation of 1.
  21. show("NormFloat64", r.NormFloat64(), r.NormFloat64(), r.NormFloat64())
  23. // Int31, Int63, and Uint32 generate values of the given width.
  24. // The Int method (not shown) is like either Int31 or Int63
  25. // depending on the size of 'int'.
  26. show("Int31", r.Int31(), r.Int31(), r.Int31())
  27. show("Int63", r.Int63(), r.Int63(), r.Int63())
  30. // Intn, Int31n, and Int63n limit their output to be < n.
  31. // They do so more carefully than using r.Int()%n.
  32. show("Intn(10)", r.Intn(10), r.Intn(10), r.Intn(10))
  33. show("Int31n(10)", r.Int31n(10), r.Int31n(10), r.Int31n(10))
  34. show("Int63n(10)", r.Int63n(10), r.Int63n(10), r.Int63n(10))
  36. // Perm generates a random permutation of the numbers [0, n).
  37. show("Perm", r.Perm(5), r.Perm(5), r.Perm(5))
  38. // Output:
  39. // Float32     0.2635776           0.6358173           0.6718283
  40. // Float64     0.628605430454327   0.4504798828572669  0.9562755949377957
  41. // ExpFloat64  0.3362240648200941  1.4256072328483647  0.24354758816173044
  42. // NormFloat64 0.17233959114940064 1.577014951434847   0.04259129641113857
  43. // Int31       1501292890          1486668269          182840835
  44. // Int63       3546343826724305832 5724354148158589552 5239846799706671610
  45. // Uint32      2760229429          296659907           1922395059
  46. // Intn(10)    1                   2                   5
  47. // Int31n(10)  4                   7                   8
  48. // Int63n(10)  7                   6                   3
  49. // Perm        [1 4 2 3 0]         [4 2 1 3 0]         [1 2 4 0 3]

Index

Package files

exp.go rand.go zipf.go

func 

  1. func ExpFloat64()

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:

  1. sample = ExpFloat64() / desiredRateParameter

func Float32

  1. func Float32() float32

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

func 

  1. func Float64()

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

func Int

  1. func Int() int

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

  1. func Int31()

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

func Int31n

  1. func Int31n(n 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

  1. func Int63() int64

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

func 

  1. func Int63n(n ) 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 

  1. func Intn(n ) 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 

  1. func NormFloat64()

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:

  1. sample = NormFloat64() * desiredStdDev + desiredMean

func Perm

  1. func Perm(n int) []

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


Example:

  1. for _, value := range rand.Perm(3) {
  2.     fmt.Println(value)
  3. }
  6. // 2
  7. // 0

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 

  1. func Seed(seed )

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

    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:

    1. words := strings.Fields("ink runs from the corners of my mouth")
    2. rand.Shuffle(len(words), func(i, j int) {
    3.     words[i], words[j] = words[j], words[i]
    4. })
    5. fmt.Println(words)
    7. // Output:
    8. // [mouth my the of runs corners from ink]


    Example:

    1. numbers := []byte("12345")
    2. letters := []byte("ABCDE")
    3. // Shuffle numbers, swapping corresponding entries in letters at the same time.
    4. rand.Shuffle(len(numbers), func(i, j int) {
    5.     numbers[i], numbers[j] = numbers[j], numbers[i]
    6.     letters[i], letters[j] = letters[j], letters[i]
    7. })
    8. for i := range numbers {
    9.     fmt.Printf("%c: %c\n", letters[i], numbers[i])
    10. }
    12. // Output:
    13. // C: 3
    14. // D: 4
    15. // A: 1
    16. // E: 5
    17. // B: 2

    func Uint32

    1. func Uint32() uint32

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

    func 

    1. func Uint64()

    Uint64 returns a pseudo-random 64-bit value as a uint64 from the default Source.

    type Rand

    1. type Rand struct {
    2.     // contains filtered or unexported fields
    3. }

    A Rand is a source of random numbers.

    func New

    1. func New(src Source) *

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

    func (*Rand) ExpFloat64

    1. func (r *Rand) ExpFloat64()

    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:

    func (*Rand) Float32

    1. func (r *Rand) Float32()

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

    func (*Rand) Float64

    1. func (r *Rand) Float64()

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

    func (*Rand) Int

    1. func (r *Rand) Int()

    Int returns a non-negative pseudo-random int.

    1. func (r *Rand) Int31()

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

    func (*Rand) Int31n

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

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

    func (*Rand)

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

    func (*Rand) 

    1. func (r *) Int63n(n int64)

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

    func (*Rand) Intn

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

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

    func (*Rand) 

    1. func (r *) 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:

    1. sample = NormFloat64() * desiredStdDev + desiredMean

    func (*Rand) 

    1. func (r *) Perm(n int) []

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

    1. func (r *Rand) Read(p []) (n int, err )

    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

    1. func (r *Rand) Seed(seed )

    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

    1. func (r *Rand) Shuffle(n , 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) 

    1. func (r *) Uint32() uint32

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

    func (*Rand) 

    1. func (r *) Uint64() uint64

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

    type 

    1. type Source interface {
    2.     Int63() 
    3.     Seed(seed int64)
    4. }

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

    func 

    1. func NewSource(seed ) 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.

    1. type Source64 interface {
    2.     
    3.     Uint64() uint64
    4. }

    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 

    1. type Zipf struct {
    2.     // contains filtered or unexported fields

    A Zipf generates Zipf distributed variates.

    func 

    1. func NewZipf(r *, s float64, v , imax uint64) *

    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.

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