Clojure - indexing a sequence without using nexts

Question

New to Clojure and trying to figure out how to index a sequence without using lots of nexts. For instance say I have the sequence:

(a b c d e f g h)

and I want to incorporate into a function the returning of the 4th item of the sequence. There must be some way besides (next (next (next sequence_name)))? So I could just pass the number 4 to the function (or any other number) and get that item from the sequence. Thanks!

leonardoborges · Accepted Answer · 2013-04-10 00:54:22Z

3

A few different ways:

(take 1 (drop 3 '(a b c d e f g h))) ;; d

(nth '(a b c d e f g h) 3) ;; d

(nth [a b c d e f g h] 3) ;; d

(nth (vec '(a b c d e f g h)) 3) ;;d

I recommend you become familiar with the sequence manipulation functions in the Clojure Cheat Sheet - it's totally worth it. Clojure's sequence library is extremely rich.

answered Apr 10, 2013 at 0:54

leonardoborges

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5 Comments

Instinct Over a year ago

Thanks for the fast answers! Was looking around the Clojure Cheat Sheet too I'll have to learn up on more of it. My only problem now is that I need to index a sequence when the sequence is stored as a variable. If I had (a b c d e f g) stored into x I've tried (nth 'x 4) and (nth '(x) 4), etc. doesn't seem to work. Or can you only index sequences directly?

Instinct Over a year ago

Also tried having "abcdefg" stored as x and then (nth '(seq x) 4) which is also apparently wrong, generating an Index out of bounds exception =/

leonardoborges Over a year ago

if it's in a variable you don't need to quote it. just try (nth x 4) and you're done :)

amalloy Over a year ago

You forgot to quote the vector [a b c d e f g h], so it evaluates to something quite different from the quoted list (a b c d e f g h).

leonardoborges Over a year ago

good point. a...h there are just placeholders for the actual values though.

Arthur Ulfeldt · Accepted Answer · 2013-04-10 00:54:46Z

2

good old nth should do the trick

user> (nth '(a b c d e f g h) 4)                                                                                                                                                   
e

(that is indexed from 0 of course)

answered Apr 10, 2013 at 0:54

Arthur Ulfeldt

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