Iterator Patterns

Map, Filter, Take, Skip in Go

Iterators Closures
2026-04-17T12:05:42+00:00
Use iter.Map, iter.Filter, iter.Take, and iter.Skip to chain lazy transformations on Go iterators for efficient data processing.

Use the iter package functions Map, Filter, Take, and Skip to chain transformations on iterators returned by functions like bytes.Lines or bytes.FieldsSeq. These functions accept an iter.Seq[T] and return a new iter.Seq[U] that applies the logic lazily.

package main

import (
	"bytes"
	"fmt"
	"iter"
	"strings"
)

func main() {
	data := []byte("line1\nline2\nline3\n")
	
	// Chain: Lines -> Filter (contains '2') -> Map (uppercase) -> Take (1)
	lines := bytes.Lines(data)
	filtered := iter.Filter(lines, func(line []byte) bool {
		return bytes.Contains(line, []byte("2"))
	})
	mapped := iter.Map(filtered, func(line []byte) string {
		return strings.ToUpper(string(line))
	})
	limited := iter.Take(mapped, 1)

	for line := range limited {
		fmt.Println(line)
	}
}