Last time I learned about maps in GO and how to create, change, and delete them. Today, I go over iterating over a map.

Iterating a Map

If I have a map of floats mapped by a string:

theMap := map[string] float64 {"1st": 1.7, "2nd" : 8.3, "3rd" 1.0 }

I can iterate the map using the syntax:

for key, value := range theMap {

}


which is similar to other languages. You can also use the underscore character to ignore either the key or value:

for _, value := range theMap { // ignore the key

}

Or you can use:

for key := range theMap { // ignore the value

}

to process just the keys.


As in other languages, GOs maps are unordered collections meaning that the items are iterated in random order.

In order (no pun intended) to loop through a map in a specific order, you can create a slice based on the map. For example, you can use the sort package.


package main

import {
"fmt"
"sort"
}


func main() {
theMap := map[string] float64 {"1st": 1.7, "2nd" : 8.3, "3rd" 1.0 }
var sorted [] float64 // create an empty slice
for key in range theMap {
sorted = append(theMap,key) // move a key from the map to the slice.
}

sort.Strings(sorted) // sort the slice of keys (strings)

for _, value := range sorted { // iterate the slice
fmt.Printf(theMap[value]) // pulling the corresponding map value
}
}


This is a pattern similar to one I might use in other languages. The one thing I'm not happy about is the first loop used to pull the keys into the slice. Most other languages have a "keys" method or property which pulls all of the keys in one step.


Those are the keys to maps. Next time, I'll start looking at structs in GO.

Tags: GO, maps, loops, Iterator