How to compare two strings alphabetically in Clojure?

Question

If I had one string that was String a = "Apple" and another that was String "b" = "Banana" how would I be able to compare the two and get something like (b > a) evaluates to true in Clojure?

Answer 1

The built-in Clojure function compare is a 3-way comparator for many kinds of values, including strings, but it compares characters by their UTF-16 Unicode code points, which for the ASCII subset will compare upper-case letters differently than lower-case letters, so maybe not what you are looking for.

If you want case-insensitive comparison between strings with all characters in the ASCII subset, you could use something like this:

(require '[clojure.string :as str])
(compare (str/lower-case s1) (str/lower-case s2))

If you want fancier locale-dependent string comparison for different languages/locale settings, there are Java libraries for that, which you can call via Java interop, e.g. see https://docs.oracle.com/javase/tutorial/i18n/text/locale.html or the ICU4J library: http://site.icu-project.org/home/why-use-icu4j

I do not know of any recommended way to replace the definitions of clojure.core/< and clojure.core/> so that they behave differently than they do for strings. You can defn them in your own code and override the definitions in clojure.core, but you will likely get warnings about doing so from the Clojure compiler. If you don't mind the warnings, go for it, but you'd better warn anyone else co-developing or using your code that you are doing so, to avoid misunderstandings.

You can define you own functions named < > etc. in your own namespace to behave however you like, of course.

Answer 2

You can find string comparison functions here, along with many other helper & convenience functions.

(increasing? a b)
Returns true if a pair of strings are in increasing lexicographic order.

(increasing-or-equal? a b)
Returns true if a pair of strings are in increasing lexicographic order, or equal.