Clojure Q&A - Recent activity in data.int-map

int-map: difference ignores its second argument when the first is itself a difference result

Fri, 02 Oct 2026 11:28:00 +0000

(require '[clojure.data.int-map :as i])

(-> (i/int-set [10 1000297])
      (i/difference (i/int-set [10]))        ;=> #{1000297}
      (i/difference (i/int-set [1000297])))  ;=> #{1000297}, expected #{}

When SingleContainer/difference removes its only element, it returns null. IntSet/difference puts that null into the tree instead of dropping the key. In the next difference, the entry with the null value goes to the else branch, which is meant for k1 > k2. That branch moves i2 forward without comparing anything, so the rest of the first set gets copied as is.

Skipping null values from the first set in that loop should fix it. So should not storing empty results in the first place. :)

Retagged: Document that clojure.data.int-map is sorted

Thu, 23 Mar 2023 15:21:41 +0000

Recently a question about it was asked on Slack.

This DIMAP-4 Jira ticket has made the map and the set deliberately sorted, but it was never mentioned in the docs.
Seems like it could be explicitly mentioned in the docstrings?

Answer selected: Should data.int-map's allow assoc'ing non-integer keys?

Fri, 27 Jan 2023 19:26:34 +0000

The stated constraint of int-map/set is that they have integer keys, and can gain performance advantages for this use case. If you want that, you should use int-map. If you don't, you should use a standard map.

So, I think it's beneficial that adding a non-int key to an int-map throws, and this should not change.

Answer selected: clojure.data.int-map could use shared empty singleton instances

Tue, 17 Jan 2023 19:26:47 +0000

Logged these as:

https://clojure.atlassian.net/browse/DIMAP-17
https://clojure.atlassian.net/browse/DIMAP-18

Answer selected: clojure.data.int-map Branch nodes allocate unused ArrayLists

Tue, 17 Jan 2023 19:26:15 +0000

Fixed for next release, thanks

Answer selected: clojure.data.int-map Branch nodes could use bitmaps to save space

Tue, 17 Jan 2023 19:25:57 +0000

Logged as https://clojure.atlassian.net/browse/DIMAP-19

`intersection` and `union` do not support `nil` punning

Tue, 31 Aug 2021 16:51:39 +0000

This is for org.clojure/data.int-map v 1.0.0.
At the same time clojure.set/intersection and clojure.set/union handle the case well.

(ns sandbox
  (:require
   [clojure.data.int-map :as int-map]
   [clojure.set]))

(clojure.set/intersection #{1 3} #{1 2 3}) ; => #{1 3}
(clojure.set/intersection #{1 3} nil) ; => nil
(clojure.set/intersection nil #{1 2 3}) ; => nil

(int-map/intersection (int-map/int-set #{1 3}) (int-map/int-set #{1 2 3})) ; => #{1 3}
(int-map/intersection (int-map/int-set #{1 3}) nil) ; => NullPointerException
(int-map/intersection nil (int-map/int-set #{1 2 3})) ; => NullPointerException

(clojure.set/union #{1 3} #{2}) ; => #{1 3 2}
(clojure.set/union #{1 3} nil) ; => #{1 3}
(clojure.set/union nil #{2}) ; => #{2}

(int-map/union (int-map/int-set #{1 3}) (int-map/int-set #{2})) ; => #{1 2 3}
(int-map/union (int-map/int-set #{1 3}) nil) ; => NullPointerException
(int-map/union nil (int-map/int-set #{2})) ; => NullPointerException

Answered: Why does PersistentPriorityMap kv-reduce call the reducing function with item and priority?

Wed, 03 Feb 2021 13:45:27 +0000

It should be a bug in there
https://github.com/clojure/data.priority-map/blob/master/src/main/clojure/clojure/data/priority_map.clj#L396

Maybe (reduce (fn [a v] (f a v k)) a [k v]) will be the right solution. Not shure

Answered: support element lookup on transient sets