Clojure Q&A - Recent questions in math.combinatorics

clojure.math.combinatorics/partitions can throw error with duplicate items and :min & :max args

Fri, 17 Feb 2023 16:04:50 +0000

When called with some duplicate items in items and with a :min & :max supplied, clojure.math.combinatorics/partitions can throw an IndexOutOfBoundsException. For example:
(dorun (clojure.math.combinatorics/partitions [1 1 2 3 4 5] :min 5 :max 5)) Execution error (IndexOutOfBoundsException) at clojure.math.combinatorics/m5$fn (combinatorics.cljc:859).
I can't replicate this when items doesn't include at least one duplicate, nor can I replicate it when :min isn't at least 5. I think :max has to be supplied, but doesn't always have to be equal to :min.
It happens with non-number items, and regardless of the order of items. It seems that it occurs when the first item is duplicated, but not for the other items.

Allow maps as multi-sets

Fri, 13 Jul 2018 11:00:12 +0000

Frequency maps are often the most natural way of expressing multi-sets in Clojure, eg. {{{:a 3 :b 2}}} is a set (unordered) of 3 {{:a}}'s and 2 {{:b}}'s: {{[:a :a :a :b :b]}}. Unfortunately, math.combinatorics currently only accepts sets in the latter form ie. a collection of possibly repeated values. It would be nice if math.combinatorics functions either supported sets represented as frequency maps or had versions which did.

Better support for sets

Sun, 12 Mar 2017 19:50:59 +0000

It seems reasonable to want to use a clojure set as the items parameter for the combinatoric functions. However, in the case of {{(combinations some-set 1)}}, an exception is raised because Clojure's distinct function (called when {{(= t 1)}}) does not support sets. This problem can be worked around by converting the set to a seq before calling combinations.

For all the other functions, it appears extending {{all-different?}} with a {{set?}} check would make the functions slightly more efficient (by avoiding the linear {{distinct?}} scan).

Support ClojureScript by converting from CLJ to CLJC

Sat, 19 Mar 2016 04:42:07 +0000

Patch attached with two changes:
1) Rename main source file to change extension from .clj to .cljc.
2) Add Clojure 1.7 dependency to pom.xml.

Ran "mvn clojure:test" and confirmed that old tests still pass.

Did not test in ClojureScript environment.

Main downside is increasing the minimum Clojure version from 1.2 to 1.7 for CLJC support. Alex Miller also indicated that the Clojure CI system was not ready for CLJC files yet, but that it would be nice to have the ticket and patch ready.

See previous clojure-dev discussion: https://groups.google.com/forum/#!topic/clojure-dev/PDyOklDEv7Y

Please add project.clj

Sun, 23 Jun 2013 23:27:44 +0000

Is there a reason for not having a project.clj in the project?

I'd like to fork, run lein test and lein repl.