This content originally appeared on DEV Community and was authored by ivan.gavlik
Vector
A vector in Clojure is an ordered, indexed, immutable collection that allows efficient random access and fast additions at the end. They are immutable.
Vectors are defined using square brackets [] or by using the vector function:
;; Creating vectors
[1 2 3 4] ;; Literal syntax
(vector 1 2 3 4) ;; Using vector function
Key Characteristics of Vectors:
Indexed (O(1) access time): You can retrieve elements using their index.
Ordered: Elements maintain the order in which they were inserted.
Immutable: Any modification creates a new vector instead of mutating the original.
Efficient addition/removal at the end: Adding elements to the end is fast (conj).
Usage & Operations:
Access Elements by Index
(def v [10 20 30 40])
(nth v 2) ;; => 30
(get v 1) ;; => 20
(v 3) ;; => 40 (Vectors can be used as functions for indexing)
Adding Elements
(conj [1 2 3] 4) ;; => [1 2 3 4] (adds to the end)
Updating Elements
(assoc [1 2 3] 1 99) ;; => [1 99 3] (Replaces index 1 with 99)
Removing Elements
Vectors do not have direct remove operations, but you can filter or use subvec:
(vec (remove #(= % 2) [1 2 3])) ;; => [1 3] (Removes 2)
(subvec [1 2 3 4] 1 3) ;; => [2 3] (Slices vector from index 1 to 2)
Iterating Over a Vector
(map inc [1 2 3]) ;; => (2 3 4)
(filter even? [1 2 3 4]) ;; => (2 4)
Sorting a Vector
(sort [3 1 4 2]) ;; => (1 2 3 4)
(sort-by count ["apple" "kiwi" "banana"]) ;; => ("kiwi" "apple" "banana") (Sort by length)
Task: Managing a Task List with Vector
Scenario:
You are building a simple task management system that stores tasks in a vector. Each task is represented as a map with the following keys:
- :id (unique task identifier)
- :title (task description)
- :priority (one of :low, :medium, :high)
- :completed? (boolean indicating if the task is done)
Goal:
Implement functions that allow you to manage tasks in the system:
Initialize Task List – Create a vector of sample tasks.
Add a Task – Insert a new task into the task list.
Remove a Task – Remove a task by its :id.
Mark a Task as Completed – Update a task’s :completed? status to true.
List All Pending Tasks – Return only tasks where :completed? is false.
Find Tasks by Priority – Retrieve all tasks with a specific priority (:low, :medium, or :high).
Sort Tasks by Priority – Sort the vector so :high priority tasks come first, followed by :medium, then :low.
Get Next Task – Return the highest-priority pending task that has not been completed.
Solution
;; Managing a Task
;; Initialize Task List
(defn init-task-list []
(hash-map {})
)
(defn valid-priority [priority]
(or (= :low priority) (= :medium priority) (= :high priority))
)
(defn create-task [id title desc priority]
(when (valid-priority priority)
{:id id :title title :description desc :priority priority :completed? false}
)
)
(defn task-not-exist? [task-list title]
(= 0 (count (filter #(= (:title %) title) task-list))
))
;; Add a Task
(defn add-task [task-list title desc priority]
(when (task-not-exist? task-list title)
(let [last-task-id (:id (last task-list) 0)
next-task-id (inc last-task-id)
task (create-task next-task-id title desc priority)]
(conj task-list task)
)
)
)
;; Remove a Task
(defn remove-task [task-list task-id]
(remove #(= (:id %) task-id) task-list)
)
;; Mark a Task as Completed
(defn mark-as-completed [task-list task-id]
(let [task (first (filter #(= (% :id) task-id) task-list))
index-of-task (index-of task-list task)]
(when (not (nil? task))
(assoc task-list index-of-task (assoc task :completed? true))
)
)
)
;; List All Pending Tasks
(defn pending-tasks [task-list]
(filter #(not (:completed? %)) task-list)
)
;; Find Tasks by Priority
(defn filter-by-priority [task-list priority]
(when (valid-priority priority)
(filter #(= (:priority %) priority) task-list)
)
)
(defn priority-count [priority]
(cond
(= priority :high) 3
(= priority :medium) 2
(= priority :low) 2
:else 0
)
)
(defn priority-higher-comparator [el1 el2] ()
(let [priority1 (priority-count (el1 :priority))
priority2 (priority-count (el2 :priority))]
(compare priority2 priority1)
)
)
;; Sort Tasks by Priority
(defn sort-by-priority [task-list]
(sort priority-higher-comparator task-list)
)
;; Get Next Task
(defn next-task [task-list]
(sort-by-priority (pending-tasks task-list))
)
This content originally appeared on DEV Community and was authored by ivan.gavlik
ivan.gavlik | Sciencx (2025-03-23T20:39:23+00:00) Practice working with Clojure vectors. Retrieved from https://www.scien.cx/2025/03/23/practice-working-with-clojure-vectors/
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