return index of a value

[Glen Rubin]

I have a vector of numbers

[0 99 3334 53 2 5 99 2 55 63]

I'd like to find the first index of a particular value. For example
if the value was 99 then I want to return 1, b/c the index of 99 is
1. I can do this with a loop/recur structure comparing each value in
the list to my desired value, however am wondering if there isn't a
built-in for doing so?? thanks again!

[Stuart Halloway]

Hi Glen,

Finding the *first* index isn't very Clojurish, what you want is to find *all* the indexes, lazily. Then if you want the first one, just call first.

(use '[clojure.contrib.seq-utils :only (positions)])
(positions #{99} [0 99 3334 53 2 5 99 2 55 63])
-> (1 6)

Cheers,
Stu

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[Michael Gardner]

In general, 'some' is used for linear searches. Given a vector 'v':

(some #(and (= 99 (v %)) %) (range 0 (count v)))

This is awkward because you're asking for the index and not the value itself. Index-based array manipulation is not often used in Clojure.

[Glen Rubin]

interesting! thx guys!