On Friday, October 22, 2021 at 6:45:18 PM UTC+2 david....@gmail.com wrote: > On Thu, Oct 21, 2021 at 5:26 AM George Neuner <gneu...@comcast.net> wrote: > >> >> On 10/20/2021 5:53 PM, unlimitedscolobb wrote: >> >> >> > You can get a lot of mileage out of the 'set' datatype, which removes > ordering from the equation, especially since lists will act as sets in a > pinch. (When you want to improve performance, use 'in-set' and/or > 'list->set'. > > To see if 2 hashes contain the same set of keys: >> >> (and (= (hash-count hash1) (hash-count hash2)) >> (for/and ([k (in-list (hash-keys hash1))]) >> (hash-has-key? hash2 k))) >> > > Alternatively: > > (set=? (hash-keys hash1) (hash-keys hash2)) > > Ah, sure, good point!
> > ; Return an unordered list of the keys that are in hash1 but not in hash2 > (set-subtract (hash-keys hash1) (hash-keys hash2)) > > ; Get a new hash consisting of the key/values that are in hash1 but not in > hash2 > (for/hash ([k (set-subtract (hash-keys hash1) (hash-keys hash2))]) > (values k (hash-ref hash1 k))) > > ; Get a ore detailed breakdown: > (require handy) > (define hash1 (for/hash ([k '(a b c d e f g)] [v 10]) (values k v))) > (define hash2 (for/hash ([k '(a b c d e z y)] [v 10]) (values k v))) > (define hash3 (hash-set* hash2 'c 111 'd 184)) > (disjunction hash1 hash3) > Result: > (dict-disjunction > '#hash((c . (2 111)) (d . (3 184))); values that differ between the hashes > '#hash((f . 5) (g . 6)) ; key/values that exist only in hash1 > '#hash((y . 6) (z . 5)) ; key/values that exist only in hash3 > '#hash((a . 0) (b . 1) (c . 2) (d . 3) (e . 4) (f . 5) (g . 6)) ; hash1 > '#hash((a . 0) (b . 1) (c . 111) (d . 3) (e . 4) (y . 6) (z . 5))) ; hash3 > > Wow, `handy` is very handy! I wasn't aware of its existence, but I'll guess you've got yourself a new user :-) > >> Unfortunately, there is no variant of "for" that creates mutable hashes. >> But the general form works for anything. >> > > If you don't mind inefficiency then handy can be, well, handy: > > (define imm-h (for/hash ([k '(a b c)][v 3]) (values k v))) > (immutable? imm-h) > (immutable? (hash->mutable imm-h)) > > hash->mutable takes an existing hash, which can be either immutable or > mutable, and adds its key/values to a new mutable hash one by one, then > returns that hash. > > Very nice! The handy module is a bit of a Fibber McGee that really needs to be broken > out. It's thoroughly documented, but unfortunately only in comments. > Converting that to proper scribble is one of my Copious Free Times projects. > > Ah, I see :-) /me looks at his own CFT projects and sighs lightly. - 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/0c1f416f-d254-4770-98e2-80f2873fc529n%40googlegroups.com.
