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What is a Map in Clojure?

Chinweuba Elijah Azubuike

Overview

A map is a collection that holds key-value pairs. The values stored in the map can be accessed using the corresponding key. In Clojure there are two types of maps:

  1. Hash maps
  2. Sorted maps

Hash maps

Hash maps are created using the hash-map function. Their keys support hashCode and equals. Let's see an example of a hash map:

Example

(ns clojure.examples.createMap
   (:gen-class))
(defn createMap []
   (def example (hash-map "x" "10" "y" "52" "z" "93"));the use of the hash-map method
   (println example))
(createMap)
Example of a hash-map

Explanation

Let's look at the explanation of the code above:

  • Line 3: We define the function createMap.
  • Line 4: We define a variable, exampleMap, and assign our map to it. The map is created using the hash-map function.
  • Line 5: We use the println to print the created map (exampleMap).
  • Line 6: We call the createMap function. This creates the hash map and prints its elements. Notice that the elements are printed in a random order.

Sorted maps

Sorted maps are created using the sorted-map function. The keys for a sorted map implement an instance of Comparable. The elements of the sorted map are sorted according to their keys. Let's take a look at an example of a sorted map:

Example

(ns clojure.examples.createSortedMap
   (:gen-class))
(defn createSortedMap []
   (def exampleMap (sorted-map "z" "10" "y" "52" "x" "93")); notice the  use of the sorted-map method
   (println exampleMap))
(createSortedMap)
An example of a sorted map

Explanation

Let's look at the explanation of the code above:

  • Line 3: We define the function keyss.
  • Line 4: We define a variable, exampleMap, and assign our map to it. We use the sorted-map method to create the map.
  • Line 5: We add a statement to print the created map using the println method.
  • Line 6: We call the createSortedMap function. This creates the sorted map and prints its elements. Notice that the elements are printed in a sorted order based on the keys.

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Chinweuba Elijah Azubuike
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