make_maps.go

package main

import (
	"fmt"
	"sort"
)

func main() {
	var mapLit map[string]int
	//var mapCreated map[string]float32
	var mapAssigned map[string]int

	mapLit = map[string]int{"one": 1, "two": 2}
	mapCreated := make(map[string]float32)
	mapAssigned = mapLit

	mapCreated["key1"] = 4.5
	mapCreated["key2"] = 3.14159
	mapAssigned["two"] = 3

	fmt.Printf("Map literal at \"one\" is: %d\n", mapLit["one"])
	fmt.Printf("Map created at \"key2\" is: %f\n", mapCreated["key2"])
	fmt.Printf("Map assigned at \"two\" is: %d\n", mapLit["two"])
	fmt.Printf("Map literal at \"two\" is: %d\n", mapLit["two"])
	fmt.Printf("Map literal at \"ten\" is: %d\n", mapLit["ten"])

	var value int
	var isPresent bool

	map1 := make(map[string]int)
	map1["New Delhi"] = 55
	map1["Beijing"] = 20
	map1["Washington"] = 25
	value, isPresent = map1["Beijing"]
	if isPresent {
		fmt.Printf("The value of \"Beijing\" in map1 is: %d\n", value)
	} else {
		fmt.Printf("map1 does not contain Beijing")
	}

	value, isPresent = map1["Paris"]
	fmt.Printf("Is \"Paris\" in map1 ?: %t\n", isPresent)
	fmt.Printf("Value is: %d\n", value)

	// delete an item:
	delete(map1, "Washington")
	value, isPresent = map1["Washington"]
	if isPresent {
		fmt.Printf("The value of \"Washington\" in map1 is: %d\n", value)
	} else {
		fmt.Println("map1 does not contain Washington")
	}

	map2 := make(map[int]float32)
	map2[1] = 1.0
	map2[2] = 2.0
	map2[3] = 3.0
	map2[4] = 4.0
	for key, value := range map2 {
		fmt.Printf("key is: %d - value is: %f\n", key, value)
	}

	// Version A:
	items := make([]map[int]int, 5)
	for i := range items {
		items[i] = make(map[int]int, 1)
		items[i][1] = 2
	}
	fmt.Printf("Version A: Value of items: %v\n", items)

	// Version B: NOT GOOD!
	items2 := make([]map[int]int, 5)
	for _, item := range items2 {
		item = make(map[int]int, 1) // item is only a copy of the slice element.
		item[1] = 2                 // This 'item' will be lost on the next iteration.
	}
	fmt.Printf("Version B: Value of items: %v\n", items2)

	var (
		barVal = map[string]int{"alpha": 34, "bravo": 56, "charlie": 23,
			"delta": 87, "echo": 56, "foxtrot": 12,
			"golf": 34, "hotel": 16, "indio": 87,
			"juliet": 65, "kili": 43, "lima": 98}
	)
	fmt.Println("unsorted:")
	for k, v := range barVal {
		fmt.Printf("Key: %v, Value: %v / ", k, v)
	}
	keys := make([]string, len(barVal))
	i := 0
	for k, _ := range barVal {
		keys[i] = k
		i++
	}
	sort.Strings(keys)
	fmt.Println()
	fmt.Println("sorted:")
	for _, k := range keys {
		fmt.Printf("Key: %v, Value: %v / ", k, barVal[k])
	}

	invMap := make(map[int]string, len(barVal))
	for k, v := range barVal {
		invMap[v] = k
	}
	fmt.Println("inverted:")
	for k, v := range invMap {
		fmt.Printf("Key: %v, Value: %v / ", k, v)
	}

}