Hi, Thank you George for your answer.
On Wednesday, October 13, 2021 at 5:37:39 PM UTC+2 gneuner2 wrote: > > On 10/12/2021 7:01 PM, unlimitedscolobb wrote: > > I wrote myself this little function: > > > > (define (hash->ordered-list h) > > (hash-map h cons #t)) > > > > which uses the try-order? argument of hash-map. > > > > Is there a reason for hash->list not have an optional argument > > try-order? Or perhaps having such a standalone function would be > better? > > > > I was planning to submit a patch, but then I thought I may be missing > > something. > > > > - > > Sergiu > > > > I can't speak for the Racket team, but ... > > Hash tables entries inherently are unordered, so there really is no > reason to expect an ordered list from reading out the data. Also, the > docs indicate that 'try-order?' doesn't work for all data types - so it > may produce unexpected results. I have two main use cases for producing an ordered list from a hash table: 1. A canonical way to pretty print a hash table: In my projects, I carry around and print out hash tables a lot, so I like the elements to appear in the same order all the time, whatever that order may be. Luckily, `hash-map` orders symbols alphabetically and numbers according to the natural order, so it's perfect for my use. 2. Testing the contents of a mutable hash table: The only way I found to that is to convert the hash table to an ordered list and compared it to the test list. This is clearly not the most efficient use of a hash table, but I can totally go with that, since it's about testing and not the actual performance. Of course, I am totally open to learning better ways of doing these things! > Further, sorting the output potentially > can take a lot of extra time ... having never tried to get ordered > output from hash-map, I can only hypothesize that (at least in some > cases) it may be faster to create the unordered list and then sort it > than to try to produce an ordered list with 'try-order?'. > I scrounged around Racket sources a bit, and even though I am not sure I looked in the right place, I got the impression that that is what hash-map with try-order? set to #t does already: creating an unordered list out of the hash table and then `sort`ing it. Certainly, you are welcome to submit a change, but I think it would be > best to leave the existing behavior and make ordered output an addition. > > FYI, here's the PR: https://github.com/racket/racket/pull/4025 I pored a lot over this, and the reasoning which won at the end was that `hash->list` is basically a call to `hash-map` with `cons` as the function to apply. Thus, adding try-order? to hash->list is a very easy change, so why not have it. Just to be clear, my PR does not alter the default behavior of `hash->list`, and only adds an optional argument. - Sergiu -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/a1e0bbd2-69f8-439e-b362-306c897926d3n%40googlegroups.com.
