In Clojure how can I convert a String to a number?

Question

I have various strings, some like \"45\", some like \"45px\". How how I convert both of these to the number 45?

Answer 1

The question asks about parsing a string into a number.

(number? 0.5)
;;=> true

So from the above decimals ought to be parsed as well.

Perhaps not exactly answering the question now, but for general use I think you would want to be strict about whether it is a number or not (so "px" not allowed) and let the caller handle non-numbers by returning nil:

(defn str->number [x]
  (when-let [num (re-matches #"-?\d+\.?\d*" x)]
    (try
      (Float/parseFloat num)
      (catch Exception _
        nil))))

And if Floats are problematic for your domain instead of Float/parseFloat put bigdec or something else.