array iteration

array iteration

Examples of iterating, mapping, filtering, and reducing arrays.

Node.js

const array = ['a', 'b', 'c']

array.forEach((value, i) => {
  console.log(i, value)
})

const mapped = array.map(value => {
  return value.toUpperCase()
})

console.log(mapped)

const filtered = array.filter((value, i) => {
  return i % 2 == 0
})

console.log(filtered)

const reduced = array.reduce((acc, value, i) => {
  if (i % 2 == 0) {
    acc.push(value.toUpperCase())
  }

  return acc
}, [])

console.log(reduced)

Output

0 'a'
1 'b'
2 'c'
[ 'A', 'B', 'C' ]
[ 'a', 'c' ]
[ 'A', 'C' ]

Go

package main

import (
    "fmt"
    "strings"
)

func main() {
    array := []string{"a", "b", "c"}

    for i, value := range array {
        fmt.Println(i, value)
    }

    mapped := make([]string, len(array))
    for i, value := range array {
        mapped[i] = strings.ToUpper(value)
    }

    fmt.Println(mapped)

    var filtered []string
    for i, value := range array {
        if i%2 == 0 {
            filtered = append(filtered, value)
        }
    }

    fmt.Println(filtered)

    var reduced []string
    for i, value := range array {
        if i%2 == 0 {
            reduced = append(reduced, strings.ToUpper(value))
        }
    }

    fmt.Println(reduced)
}

Output

0 a
1 b
2 c
[A B C]
[a c]
[A C]