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Go Basics

Go Maps

Store values under keys: add, read, check, delete and loop in a fixed order.

  • Beginner
  • 3 min read
  • 1 runnable example
What you'll learn
  • Creating and updating
  • The value, ok form
  • Sorting the keys
Run code →
stock
"apple"5
"pear"5
"plum"1

Values found by key

A map stores values under keys, so you can find a value quickly by its key. It is Go's version of a dictionary or hash table.

Reading a missing key returns the zero value, so the second result, found, tells you whether the key exists. delete removes a key. A map has no fixed order, so the keys are collected and sorted before printing.

Key points

  1. A missing key reads as the zero value.
  2. value, found := m[key] tells you if it exists.
  3. Map order is random: sort the keys.

Runnable Go example

Go
Run code →
main.go
package main

import (
	"fmt"
	"sort"
)

func main() {
	stock := map[string]int{"apple": 3, "pear": 5}
	stock["plum"] = 1
	stock["apple"] += 2

	fmt.Println(stock["apple"], len(stock))

	count, found := stock["kiwi"]
	fmt.Println(count, found)

	delete(stock, "pear")

	names := make([]string, 0, len(stock))
	for name := range stock {
		names = append(names, name)
	}
	sort.Strings(names) // map order is random, so sort the keys
	for _, name := range names {
		fmt.Println(name, stock[name])
	}
}
Get a Run button for this example Result of running the code
5 3
0 false
apple 5
plum 1

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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