# \#data-structures
**URL:** https://racket.discourse.group/tag/data-structures/192.md
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## [Difference Lists and Racket](https://racket.discourse.group/t/difference-lists-and-racket/3184)
**Author:** [@shawnw](https://racket.discourse.group/u/shawnw)\
**Replies:** 3\
**Last updated:** [October 6, 2024, 10:07pm UTC](https://racket.discourse.group/t/difference-lists-and-racket/3184 "2024-10-06T22:07:11Z")
Something I've been playing with and wanted to share. If you're building up a final list by appending intermediate ones together, it's easy to get quadratic behavior if you're not careful - appending to the end of a con…
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## [Efficiently updating nested data structures in Racket](https://racket.discourse.group/t/efficiently-updating-nested-data-structures-in-racket/2877)
**Author:** [@rvdalen](https://racket.discourse.group/u/rvdalen)\
**Replies:** 12\
**Last updated:** [April 27, 2024, 8:09pm UTC](https://racket.discourse.group/t/efficiently-updating-nested-data-structures-in-racket/2877 "2024-04-27T20:09:06Z")
I am trying to write some code that updates immutable nested data structures. There does not seem to be good support for this in base Racket, and the internet seems to point to using the lens library for this. The lens…
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## [Using Hash-Tables as Multisets](https://racket.discourse.group/t/using-hash-tables-as-multisets/2333)
**Author:** [@bakgatviooldoos](https://racket.discourse.group/u/bakgatviooldoos)\
**Replies:** 1\
**Last updated:** [September 23, 2023, 9:15am UTC](https://racket.discourse.group/t/using-hash-tables-as-multisets/2333 "2023-09-23T09:15:32Z")
Hi, Racket Discourse. I have been thinking a lot about multisets recently, because I want to implement a particular "computer algebra" system which codifies arithmetic/algebra in terms of "closed-form numbers", to a deg…