On Tue, Aug 23, 2011 at 09:44, Mark Engelberg <[email protected]> wrote:
> I had always assumed that vectors were sorted lexicographically. In
> other words, you sort on the first element, and then refine by the
> second element, and so on. I was surprised tonight to discover that
> is not the case.
>
>> (compare "abc" "b") ; Strings are compared lexicographically
> -1
>> (compare (vec "abc") (vec "b")) ; Vectors are not
> 1
>
> It turns out that shorter vectors are always considered to be "less
> than" longer vectors. Lexicographic behavior only kicks in among
> vectors of the same length. Not at all what I expected, so I wanted
> to make sure everyone knew about this behavior.
Yea, confirmed.
$ git describe
clojure-1.3.0-beta1-6-g82c7254
$ java -jar target/clojure-1.3.0-master-SNAPSHOT.jar
Clojure 1.3.0-master-SNAPSHOT
user=> (defn sort* [ & more ] (sort more))
;; strings: always sort lexicographically
user=> (sort* "abc" "b")
("abc" "b")
;; vector: short sorts before long
user=> (sort* (vec "abc") (vec "b"))
([\b] [\a \b \c])
;; vector: same length sorts lexicographically
user=> (sort* (vec "abc") (vec "abb"))
([\a \b \b] [\a \b \c])
user=> (sort* (vec "abc") (vec "abd"))
([\a \b \c] [\a \b \d])
;; seq: does not implement comparable
user=> (sort* (seq "abc") (seq "b"))
ClassCastException clojure.lang.StringSeq cannot be cast to
java.lang.Comparable clojure.lang.Util.compare (Util.java:92)
user=> (sort* (seq (vec "abc")) (seq (vec "b")))
ClassCastException clojure.lang.PersistentVector$ChunkedSeq cannot be
cast to java.lang.Comparable clojure.lang.Util.compare (Util.java:92)
;; list: does not implement comparable
user=> (sort* (apply list "abc") (apply list "b"))
ClassCastException clojure.lang.PersistentList cannot be cast to
java.lang.Comparable clojure.lang.Util.compare (Util.java:92)
It seems a shame that Clojure doesn't provide universal lexicographical
comparability of sequential things, much as it provides equality for
sequential things:
user=> (= (list \a \b \c) (vector \a \b \c))
true
Perhaps there's a good reason for this (law of unintended consequences,
anyone?) that I'm not seeing.
// Ben
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