Accessing and updating elements from collections

In this recipe, we will teach you how to access elements and update elements in collections.

Getting ready

You only need REPL, as described in the recipe in Chapter 1, Live Programming with Clojure, and no additional libraries. Start REPL so that you can review the sample code in this recipe.

How to do it...

Let's start with accessing collections.

Accessing collections using the nth function

nth gets the n^th element from collections. The second argument of nth starts from 0 and throws an exception if the second argument is larger than the number of elements minus 1:

(nth [1 2 3 4 5] 1) 
;;=> 2 
(nth '("a" "b" "c" "d" "e") 3) 
;;=> "d" 
(nth [1 2 3] 3) 
;;=> IndexOutOfBoundsException   clojure.lang.PersistentVector.arrayFor (PersistentVector.java:153) 

If you would like to avoid such an exception, use the third argument as the return value:

(nth [1 2 3] 3 nil) 
;;=> nil 

Notice that nth does not...