Using a map of slices without initialization

main.go

package main

import "fmt"

type person struct {
	name string
	age  int
}

func main() {
	people := []person{
		{"Jim", 7},
		{"Janna", 5},
		{"Jake", 5},
		{"Joseph", 7},
		{"Jennifer", 5},
	}

	histogram := make(map[int][]string)

	for _, p := range people {
		histogram[p.age] = append(histogram[p.age], p.name)
	}

	// map[5:[Janna Jake Jennifer] 7:[Jim Joseph]]
	fmt.Println(histogram)
}