rand
packagestandard library
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Documentation¶
Overview¶
Package rand implements pseudo-random number generators suitable for taskssuch as simulation, but it should not be used for security-sensitive work.
Random numbers are generated by aSource, usually wrapped in aRand.Both types should be used by a single goroutine at a time: sharing amongmultiple goroutines requires some kind of synchronization.
Top-level functions, such asFloat64 andInt,are safe for concurrent use by multiple goroutines.
This package's outputs might be easily predictable regardless of how it'sseeded. For random numbers suitable for security-sensitive work, see thecrypto/rand package.
Example¶
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))])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.
// Create and seed the generator.// Typically a non-fixed seed should be used, such as Uint64(), Uint64().// Using a fixed seed will produce the same output on every run.r := rand.New(rand.NewPCG(1, 2))// 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 any) {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())// Int32, Int64, and Uint32 generate values of the given width.// The Int method (not shown) is like either Int32 or Int64// depending on the size of 'int'.show("Int32", r.Int32(), r.Int32(), r.Int32())show("Int64", r.Int64(), r.Int64(), r.Int64())show("Uint32", r.Uint32(), r.Uint32(), r.Uint32())// IntN, Int32N, and Int64N 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("Int32N(10)", r.Int32N(10), r.Int32N(10), r.Int32N(10))show("Int64N(10)", r.Int64N(10), r.Int64N(10), r.Int64N(10))// Perm generates a random permutation of the numbers [0, n).show("Perm", r.Perm(5), r.Perm(5), r.Perm(5))Output:Float32 0.95955694 0.8076733 0.8135684Float64 0.4297927436037299 0.797802349388613 0.3883664855410056ExpFloat64 0.43463410545541104 0.5513632046504593 0.7426404617374481NormFloat64 -0.9303318111676635 -0.04750789419852852 0.22248301107582735Int32 2020777787 260808523 851126509Int64 5231057920893523323 4257872588489500903 158397175702351138Uint32 314478343 1418758728 208955345IntN(10) 6 2 0Int32N(10) 3 7 7Int64N(10) 8 9 4Perm [0 3 1 4 2] [4 1 2 0 3] [4 3 2 0 1]
Index¶
- func ExpFloat64() float64
- func Float32() float32
- func Float64() float64
- func Int() int
- func Int32() int32
- func Int32N(n int32) int32
- func Int64() int64
- func Int64N(n int64) int64
- func IntN(n int) int
- func N[Int intType](n Int) Int
- func NormFloat64() float64
- func Perm(n int) []int
- func Shuffle(n int, swap func(i, j int))
- func Uint() uint
- func Uint32() uint32
- func Uint32N(n uint32) uint32
- func Uint64() uint64
- func Uint64N(n uint64) uint64
- func UintN(n uint) uint
- type ChaCha8
- type PCG
- type Rand
- func (r *Rand) ExpFloat64() float64
- func (r *Rand) Float32() float32
- func (r *Rand) Float64() float64
- func (r *Rand) Int() int
- func (r *Rand) Int32() int32
- func (r *Rand) Int32N(n int32) int32
- func (r *Rand) Int64() int64
- func (r *Rand) Int64N(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) Shuffle(n int, swap func(i, j int))
- func (r *Rand) Uint() uint
- func (r *Rand) Uint32() uint32
- func (r *Rand) Uint32N(n uint32) uint32
- func (r *Rand) Uint64() uint64
- func (r *Rand) Uint64N(n uint64) uint64
- func (r *Rand) UintN(n uint) uint
- type Source
- type Zipf
Examples¶
Constants¶
This section is empty.
Variables¶
This section is empty.
Functions¶
funcExpFloat64¶
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
funcFloat32¶
func Float32()float32
Float32 returns, as a float32, a pseudo-random number in the half-open interval [0.0,1.0)from the default Source.
funcFloat64¶
func Float64()float64
Float64 returns, as a float64, a pseudo-random number in the half-open interval [0.0,1.0)from the default Source.
funcInt32¶
func Int32()int32
Int32 returns a non-negative pseudo-random 31-bit integer as an int32from the default Source.
funcInt32N¶
Int32N returns, as an int32, a pseudo-random number in the half-open interval [0,n)from the default Source.It panics if n <= 0.
funcInt64¶
func Int64()int64
Int64 returns a non-negative pseudo-random 63-bit integer as an int64from the default Source.
funcInt64N¶
Int64N returns, as an int64, a pseudo-random number in the half-open interval [0,n)from the default Source.It panics if n <= 0.
funcIntN¶
IntN returns, as an int, a pseudo-random number in the half-open interval [0,n)from the default Source.It panics if n <= 0.
Example¶
fmt.Println(rand.IntN(100))fmt.Println(rand.IntN(100))fmt.Println(rand.IntN(100))
funcN¶
func N[Int intType](n Int) Int
N returns a pseudo-random number in the half-open interval [0,n) from the default Source.The type parameter Int can be any integer type.It panics if n <= 0.
Example¶
// Print an int64 in the half-open interval [0, 100).fmt.Println(rand.N(int64(100)))// Sleep for a random duration between 0 and 100 milliseconds.time.Sleep(rand.N(100 * time.Millisecond))
funcNormFloat64¶
func NormFloat64()float64
NormFloat64 returns a normally distributed float64 in the range[-math.MaxFloat64, +math.MaxFloat64] withstandard normal distribution (mean = 0, stddev = 1)from the default Source.To produce a different normal distribution, callers canadjust the output using:
sample = NormFloat64() * desiredStdDev + desiredMean
funcPerm¶
Perm returns, as a slice of n ints, a pseudo-random permutation of the integersin the half-open interval [0,n) from the default Source.
Example¶
for _, value := range rand.Perm(3) {fmt.Println(value)}Output:120
funcShuffle¶
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)Example (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])}funcUint32¶
func Uint32()uint32
Uint32 returns a pseudo-random 32-bit value as a uint32from the default Source.
funcUint32N¶
Uint32N returns, as a uint32, a pseudo-random number in the half-open interval [0,n)from the default Source.It panics if n == 0.
funcUint64¶
func Uint64()uint64
Uint64 returns a pseudo-random 64-bit value as a uint64from the default Source.
Types¶
typeChaCha8¶
type ChaCha8 struct {// contains filtered or unexported fields}A ChaCha8 is a ChaCha8-based cryptographically strongrandom number generator.
funcNewChaCha8¶
NewChaCha8 returns a new ChaCha8 seeded with the given seed.
func (*ChaCha8)AppendBinary¶added ingo1.24.0
AppendBinary implements theencoding.BinaryAppender interface.
func (*ChaCha8)MarshalBinary¶
MarshalBinary implements theencoding.BinaryMarshaler interface.
func (*ChaCha8)Read¶added ingo1.23.0
Read reads exactly len(p) bytes into p.It always returns len(p) and a nil error.
If calls to Read and Uint64 are interleaved, the order in which bits arereturned by the two is undefined, and Read may return bits generated beforethe last call to Uint64.
func (*ChaCha8)UnmarshalBinary¶
UnmarshalBinary implements theencoding.BinaryUnmarshaler interface.
typePCG¶
type PCG struct {// contains filtered or unexported fields}A PCG is a PCG generator with 128 bits of internal state.A zero PCG is equivalent to NewPCG(0, 0).
func (*PCG)AppendBinary¶added ingo1.24.0
AppendBinary implements theencoding.BinaryAppender interface.
func (*PCG)MarshalBinary¶
MarshalBinary implements theencoding.BinaryMarshaler interface.
func (*PCG)UnmarshalBinary¶
UnmarshalBinary implements theencoding.BinaryUnmarshaler interface.
typeRand¶
type Rand struct {// contains filtered or unexported fields}A Rand is a source of random numbers.
func (*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:
sample = ExpFloat64() / desiredRateParameter
func (*Rand)Float32¶
Float32 returns, as a float32, a pseudo-random number in the half-open interval [0.0,1.0).
func (*Rand)Float64¶
Float64 returns, as a float64, a pseudo-random number in the half-open interval [0.0,1.0).
func (*Rand)Int32N¶
Int32N returns, as an int32, a non-negative pseudo-random number in the half-open interval [0,n).It panics if n <= 0.
func (*Rand)Int64N¶
Int64N returns, as an int64, a non-negative pseudo-random number in the half-open interval [0,n).It panics if n <= 0.
func (*Rand)IntN¶
IntN returns, as an int, a non-negative pseudo-random number in the half-open interval [0,n).It panics if n <= 0.
func (*Rand)NormFloat64¶
NormFloat64 returns a normally distributed float64 inthe range -math.MaxFloat64 through +math.MaxFloat64 inclusive,with standard normal distribution (mean = 0, stddev = 1).To produce a different normal distribution, callers canadjust the output using:
sample = NormFloat64() * desiredStdDev + desiredMean
func (*Rand)Perm¶
Perm returns, as a slice of n ints, a pseudo-random permutation of the integersin the half-open interval [0,n).
func (*Rand)Shuffle¶
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)Uint32N¶
Uint32N returns, as a uint32, a non-negative pseudo-random number in the half-open interval [0,n).It panics if n == 0.
typeSource¶
type Source interface {Uint64()uint64}A Source is a source of uniformly-distributedpseudo-random uint64 values in the range [0, 1<<64).
A Source is not safe for concurrent use by multiple goroutines.
Source Files