Documentation

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.

    Mathematical interval notation such as [0, n) is used throughout the documentation for this package.

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

    Example
    Output:
    
    Magic 8-Ball says: As I see it yes
    
    Example (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.

      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

      Examples

      Constants

      This section is empty.

      Variables

      This section is empty.

      Functions

      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.

                        Example
                        Output:
                        
                        42
                        76
                        30
                        

                        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
                            Output:
                            
                            1
                            2
                            0
                            

                            func Read added in go1.6

                            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 2³¹-1 generate the same pseudo-random sequence. Seed, unlike the Rand.Seed method, is safe for concurrent use.

                                func Shuffle added in go1.10

                                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
                                  Output:
                                  
                                  [mouth my the of runs corners from ink]
                                  
                                  Example (SlicesInUnison)
                                  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 added in go1.8

                                    func Uint64() uint64

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

                                      Types

                                      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 through +math.MaxFloat64 inclusive, 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 added in go1.6

                                                                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 added in go1.10

                                                                    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 added in go1.8

                                                                        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 added in go1.8

                                                                              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.