Group By in Go

package main

import (
    "fmt"
)

func main() {
    a := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
    // Here, we know how many paritions we need for grouping by even/odd numbers.
    partitions := make([][]int, 2)
    for _, n := range a {
        idx := n % 2
        partitions[idx] = append(partitions[idx], n)
    }
    fmt.Println(partitions)

    // Next we try grouping by first letter of a word.
    // Here, we use a map to access buckets by a key.
    b := []string{"orange", "apple", "grapefruit", "avocados"}
    partitions2 := map[string][]string{}
    for _, str := range b {
        key := string(str[0])
        partitions2[key] = append(partitions2[key], str)
    }
    fmt.Println(partitions2)
}