Sunday, June 3, 2012

Tour golang Exercise: Maps #45 WordCount Solution



This exercise from the golang tour asks for a function that will count the number of times each word appears in a string. I think of it as using a hash to contain a histogram of word frequency. The if/else could be tighter if go had a ternary operator.


Code:


package main

import "strings"
import "fmt"

func WordCount (s string) map[string]int {

    substrs := strings.Fields(s)
    fmt.Println(substrs)

    // key,value  ==> word,count
    // iterate over substrs, if key in map, value++, else create

    counts := make(map[string]int)

    for _, word := range substrs {
        _, ok := counts[word]

        if ok == true {
          counts[word] += 1
        } else {
          counts[word] = 1
        }
    }

    return counts
}

func main() {
  fmt.Println(WordCount("now is the now is the go go go it a a a a a"))
  fmt.Println(WordCount("1 2 3 11 22 33 1 2 3"))
}

Output:

[now is the now is the go go go it a a a a a]
map[now:2 the:2 go:3 a:5 is:2 it:1]
[1 2 3 11 22 33 1 2 3]
map[2:2 33:1 1:2 11:1 22:1 3:2]

Common Error:

./wordcount2.go:20: cannot convert true to type int
./wordcount2.go:20: invalid operation: ok == true (mismatched types int and bool)

This occurs when attempting: 

    ok := counts[word]

Instead of:
    
    _, ok := counts[word]

5 comments:

  1. Hey Kevin

    I had the same solution you did, but noticed you don't need the conditional since you already defined you map to have element types of int. You can simply update your map as so

    counts[word] += 1

    Also, if you were to use the if statement, you can use the shorthand !ok since you are testing a boolean value.

    I made a gist for my solution here: https://gist.github.com/3158788

    Kindest regards

    Thomas Frederiksen

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