On Friday, October 22, 2021 at 6:45:18 PM UTC+2 [email protected] wrote: > On Thu, Oct 21, 2021 at 5:26 AM George Neuner <[email protected]> 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/0c1f416f-d254-4770-98e2-80f2873fc529n%40googlegroups.com.
