Question

I’ve been using java to parse numbers, e.g.

(. Integer parseInt  numberString)

Is there a more clojuriffic way that would handle both integers and floats, and return clojure numbers? I’m not especially worried about performance here, I just want to process a bunch of white space delimited numbers in a file and do something with them, in the most straightforward way possible.

So a file might have lines like:

5  10  0.0002
4  12  0.003

And I’d like to be able to transform the lines into vectors of numbers.

Answer 1

You can use the edn reader to parse numbers. This has the benefit of giving you floats or Bignums when needed, too.

user> (require '[clojure.edn :as edn])
nil
user> (edn/read-string "0.002")
0.0020

If you want one huge vector of numbers, you could cheat and do this:

user> (let [input "5  10  0.002\n4  12  0.003"]
        (read-string (str "[" input "]")))
[5 10 0.0020 4 12 0.0030]

Kind of hacky though. Or there’s re-seq:

user> (let [input "5  10  0.002\n4  12  0.003"]
        (map read-string (re-seq #"[\d.]+" input)))
(5 10 0.0020 4 12 0.0030)

Or one vector per line:

user> (let [input "5  10  0.002\n4  12  0.003"]
        (for [line (line-seq (java.io.BufferedReader.
                              (java.io.StringReader. input)))]
             (vec (map read-string (re-seq #"[\d.]+" line)))))
([5 10 0.0020] [4 12 0.0030])

I’m sure there are other ways.