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filters.go
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filters.go
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package stream
import "fmt"
// Items emits items.
func Items(items ...string) Filter {
return FilterFunc(func(arg Arg) error {
for _, s := range items {
arg.Out <- s
}
return nil
})
}
// Repeat emits n copies of s.
func Repeat(s string, n int) Filter {
return FilterFunc(func(arg Arg) error {
for i := 0; i < n; i++ {
arg.Out <- s
}
return nil
})
}
// Numbers emits the integers x..y
func Numbers(x, y int) Filter {
return FilterFunc(func(arg Arg) error {
for i := x; i <= y; i++ {
arg.Out <- fmt.Sprint(i)
}
return nil
})
}
// Map calls fn(x) for every item x and yields the outputs of the fn calls.
func Map(fn func(string) string) Filter {
return FilterFunc(func(arg Arg) error {
for s := range arg.In {
arg.Out <- fn(s)
}
return nil
})
}
// If emits every input x for which fn(x) is true.
func If(fn func(string) bool) Filter {
return FilterFunc(func(arg Arg) error {
for s := range arg.In {
if fn(s) {
arg.Out <- s
}
}
return nil
})
}
// Uniq squashes adjacent identical items in arg.In into a single output.
func Uniq() Filter {
return FilterFunc(func(arg Arg) error {
first := true
last := ""
for s := range arg.In {
if first || last != s {
arg.Out <- s
}
last = s
first = false
}
return nil
})
}
// UniqWithCount squashes adjacent identical items in arg.In into a single
// output prefixed with the count of identical items followed by a space.
func UniqWithCount() Filter {
return FilterFunc(func(arg Arg) error {
current := ""
count := 0
for s := range arg.In {
if s != current {
if count > 0 {
arg.Out <- fmt.Sprintf("%d %s", count, current)
}
count = 0
current = s
}
count++
}
if count > 0 {
arg.Out <- fmt.Sprintf("%d %s", count, current)
}
return nil
})
}
// Reverse yields items in the reverse of the order it received them.
func Reverse() Filter {
return FilterFunc(func(arg Arg) error {
var data []string
for s := range arg.In {
data = append(data, s)
}
for i := len(data) - 1; i >= 0; i-- {
arg.Out <- data[i]
}
return nil
})
}
// NumberLines prefixes its item with its index in the input sequence
// (starting at 1) followed by a space.
func NumberLines() Filter {
return FilterFunc(func(arg Arg) error {
line := 1
for s := range arg.In {
arg.Out <- fmt.Sprintf("%5d %s", line, s)
line++
}
return nil
})
}
// Columns splits each item into columns and yields the concatenation
// (separated by spaces) of the columns numbers passed as arguments.
// Columns are numbered starting at 1. If a column number is bigger
// than the number of columns in an item, it is skipped.
func Columns(columns ...int) Filter {
return FilterFunc(func(arg Arg) error {
for _, c := range columns {
if c <= 0 {
return fmt.Errorf("stream.Columns: invalid column number %d", c)
}
}
for s := range arg.In {
result := ""
for _, col := range columns {
if _, c := column(s, col); c != "" {
if result != "" {
result = result + " "
}
result = result + c
}
}
arg.Out <- result
}
return nil
})
}