I'm trying to get a code to work that pretty much involves channels in goroutine (in a yield-like behavior in C#)
The code involves getting an iterable matrix from a slice like so:
elements := []float64{1, 2, 3, 4}
expected := [][]float64{
{1},
{2},
{3},
{4},
{1, 2},
{1, 3},
{2, 3},
{1, 4},
{2, 4},
{3, 4},
{1, 2, 3},
{1, 2, 4},
{1, 3, 4},
{2, 3, 4},
{1, 2, 3, 4},
}
I've tried applying Knuth's by doing:
func Combinadic(values []float64) <-chan []float64 {
ch := make(chan []float64)
go func() {
for i := 0; i < len(values); i++ {
for value := range CombinadicK(values, i+1) {
ch <- value
}
}
close(ch)
}()
return ch
}
func CombinadicK(values []float64, k int) <-chan []float64 {
chnl := make(chan []float64)
go func() {
n := len(values)
t := k
c := make([]int, t+3)
current := make([]float64, t)
x := 0
j := 0
for j = 1; j <= t; j++ {
c[j] = j - 1
}
c[t+1] = n
c[t+2] = 0
j = t
for {
for i := 0; i < len(current); i++ {
current[i] = values[c[i+1]]
}
chnl <- current
if j > 0 {
x = j
} else {
if c[1]+1 < c[2] {
c[1]++
continue
} else {
j = 2
}
}
for {
c[j-1] = j - 2
x = c[j] + 1
if x == c[j+1] {
j++
} else {
break
}
}
c[j] = x
j--
if j >= t {
break
}
}
close(chnl)
}()
return chnl
}
It appears to give out random number per row, but the structure of the expected (the count of items per row) appears to be ok.
The code in Go Playground
You have a data race. Your results are undefined.
$ go run -race racer.go
==================
WARNING: DATA RACE
Read at 0x00c00009c010 by main goroutine:
reflect.typedmemmove()
/home/peter/go/src/runtime/mbarrier.go:177 +0x0
reflect.packEface()
/home/peter/go/src/reflect/value.go:119 +0x103
reflect.valueInterface()
/home/peter/go/src/reflect/value.go:1027 +0x16f
fmt.(*pp).printValue()
/home/peter/go/src/reflect/value.go:997 +0x38f7
fmt.(*pp).printValue()
/home/peter/go/src/fmt/print.go:868 +0xec7
fmt.(*pp).printArg()
/home/peter/go/src/fmt/print.go:715 +0x2ee
fmt.(*pp).doPrintln()
/home/peter/go/src/fmt/print.go:1172 +0xad
fmt.Fprintln()
/home/peter/go/src/fmt/print.go:263 +0x65
main.main()
/home/peter/go/src/fmt/print.go:273 +0x14b
Previous write at 0x00c00009c010 by goroutine 8:
main.CombinadicK.func1()
/home/peter/racer.go:48 +0x1e6
Goroutine 8 (running) created at:
main.CombinadicK()
/home/peter/racer.go:26 +0x96
main.Combinadic.func1()
/home/peter/racer.go:12 +0xda
==================
[3]
[3]
[4]
[4]
[2 3]
[2 4]
[1 4]
[3 4]
[3 4]
[3 4]
[1 3 4]
[1 3 4]
[1 3 4]
[2 3 4]
[1 2 3 4]
Found 1 data race(s)
exit status 66
$
racer.go:
package main
import (
"fmt"
)
func Combinadic(values []float64) <-chan []float64 {
ch := make(chan []float64)
go func() {
for i := 0; i < len(values); i++ {
for value := range CombinadicK(values, i+1) {
ch <- value
}
}
close(ch)
}()
return ch
}
func CombinadicK(values []float64, k int) <-chan []float64 {
chnl := make(chan []float64)
go func() {
n := len(values)
t := k
c := make([]int, t+3)
current := make([]float64, t)
x := 0
j := 0
for j = 1; j <= t; j++ {
c[j] = j - 1
}
c[t+1] = n
c[t+2] = 0
j = t
for {
for i := 0; i < len(current); i++ {
current[i] = values[c[i+1]]
}
chnl <- current
if j > 0 {
x = j
} else {
if c[1]+1 < c[2] {
c[1]++
continue
} else {
j = 2
}
}
for {
c[j-1] = j - 2
x = c[j] + 1
if x == c[j+1] {
j++
} else {
break
}
}
c[j] = x
j--
if j >= t {
break
}
}
close(chnl)
}()
return chnl
}
func main() {
elements := []float64{1, 2, 3, 4}
for v := range Combinadic(elements) {
fmt.Println(v)
}
}
Playground: https://play.golang.org/p/hhQgVdqe6l1