Go Practice Exercises

Word Frequency Counter in Go

Count how often each word appears with a map and print the most common ones.

Beginner
3 min read
1 runnable example

What you'll learn

strings.Fields
counts[word]++
Sorting by count

Run code →

counts

"the"3

"brown"1

"dog"1

The word is the key, the count is the value

Counting words is a typical job for a map: the word is the key and the number of times it appears is the value.

counts[word]++ works even for a new word, because a missing key reads as 0. The words are then sorted by count, highest first, and alphabetically when the counts are equal, so the output is always the same.

Key points

A missing key reads as 0, so ++ just works.
Sort by count, then by word.
words[:3] keeps the top three.

Runnable Go example

Run code →

main.go

package main

import (
	"fmt"
	"sort"
	"strings"
)

func main() {
	text := "the quick brown fox jumps over the lazy dog the end"
	counts := map[string]int{}
	for _, word := range strings.Fields(text) {
		counts[word]++
	}

	words := make([]string, 0, len(counts))
	for word := range counts {
		words = append(words, word)
	}
	sort.Slice(words, func(i, j int) bool {
		if counts[words[i]] != counts[words[j]] {
			return counts[words[i]] > counts[words[j]]
		}
		return words[i] < words[j]
	})

	for _, word := range words[:3] {
		fmt.Printf("%s: %d\n", word, counts[word])
	}
}

Get a Run button for this example Result of running the code

the: 3
brown: 1
dog: 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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