Question about traversing a list

Question

Hi, I am a beginner in Clojure, and I have a simple question

Lets say i have a List, composed of Maps. Each Map has a :name and :age

My code is:

(def Person {:nom rob :age 31 } ) (def Persontwo {:nom sam :age 80 } ) (def Persontthree {:nom jim :age 21 } ) (def mylist (list Person Persontwo Personthree))

Now how do i traverse the list. Let's say for example, that i have a given :name. How do i traverse the list to see if any of the Maps :name matches my :name. And then if there is a map that matches, how do i get the index position of that map?

-Thank you

Answer 1

(defn find-person-by-name [name people] 
   (let
      [person (first (filter (fn [person] (= (get person :nom) name)) people))]
      (print (get person :nom))
      (print (get person :age))))

EDIT: the above was the answer to the question as it was before question was edited; here's the updated one - filter and map were starting to get messy, so I rewrote it from scratch using loop:

; returns 0-based index of item with matching name, or nil if no such item found
(defn person-index-by-name [name people] 
    (loop [i 0 [p & rest] people]
        (cond
            (nil? p)
                nil
            (= (get p :nom) name) 
                i
            :else
                (recur (inc i) rest))))

Answer 2

This can be done with doseq:

(defn print-person [name people]
  (doseq [person people]
    (when (= (:nom person) name)
      (println name (:age person)))))

Answer 3

I would suggest looking at the filter function. This will return a sequence of items that match some predicate. As long as you don't have name duplication (and your algorithm would seem to dictate this), it would work.

Answer 4

Since you changed your question I give you a new answer. (I don't want to edit my old answer since that would make the comments very confusing).

There might be a better way to do this...

(defn first-index-of [key val xs]
  (loop [index 0
         xs xs]
    (when (seq xs)
      (if (= (key (first xs)) val)
        index
        (recur (+ index 1)
               (next xs))))))

This function is used like this:

> (first-index-of :nom 'sam mylist)
1
> (first-index-of :age 12 mylist)
nil
> (first-index-of :age 21 mylist)
2