Question

Consider the following:

=> (even? (count []))
true

so far so good. Now consider (assume my-file is empty):

(odd? (count (str/split (slurp my-file) #"\|")))
true

err … why is the vector returned from an empty file not even (zero) ?

=>(str/split (slurp my-file) #"\|")
[""]

Ahh, can someone explain why an empty string is returned in this case?

I’m attempting to determine if there are an odd number of records in a file or not.

Answer 1

clojure.string/split uses java.util.regex.Pattern/split to do the splitting. See this question about Java for explanation. Namely, split returns everything before the first match of your pattern as the first split, even if the pattern doesn’t match at all.

The canonical way to test if a collection (list,array,map,string etc.) is empty or not is to call seq on it, which will return nil for an empty collection.

(defn odd-number-of-records? [filename]
  (let [txt (slurp filename)]
    (when (seq txt)
      (odd? (count (str/split txt #"\|"))))))