Is there any default way to append hashes?

Is there any default way to append hashes?

[Jean Louis]

I am using this function to append hashes, is there maybe some better
or default method?

(defun hash-append (h1 h2)
  "Append hash H2 to H1 and return H1."
  (maphash (lambda (key value) (puthash key value h1)) h2)
  h1)



Jean

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Re: Is there any default way to append hashes?

[Stefan Monnier]

> I am using this function to append hashes, is there maybe some better
> or default method?

Maybe you're looking for `map-merge`?


        Stefan


PS: I actually had to look at your code to understand what you meant,
    because to me this is not "appending" and it's not operating on
    "hash"es (but on "hash tables").

Re: Is there any default way to append hashes?

[Jean Louis]

* Stefan Monnier <monnier@iro.umontreal.ca> [2021-05-03 19:18]:
> > I am using this function to append hashes, is there maybe some better
> > or default method?
> 
> Maybe you're looking for `map-merge`?

Thank you.

I have tried best to find something like that but could not. In the
mean time I made the function below, and it does append or join keys
and values from other hashes to the first one.

Yes, I needed function to append or join other hashes to the first
one which is being used. Now I know `map-merge' I can use it.

(defun hash-append (h1 &rest hashes)
  "Return H1 hash appende with HASHES."
  (mapc 
   (lambda (hash)
     (maphash 
      (lambda (key value) (puthash key value h1)) hash))
   hashes)
  h1)

(setq h1 (make-hash-table :test 'equal))
(setq h2 (make-hash-table :test 'equal))
(puthash 'name "Jimmy" h1)
(puthash "last" "Lorence" h1)
(puthash "age" 12 h2)
(puthash "city" "New York" h2)

(hash-append h1 h2) ⇒ #s(hash-table size 65 test equal rehash-size 1.5 rehash-threshold 0.8125 data (name "Jimmy" "last" "Lorence" "age" 12 "city" "New York"))

h1 ⇒ #s(hash-table size 65 test equal rehash-size 1.5 rehash-threshold 0.8125 data (name "Jimmy" "last" "Lorence" "age" 12 "city" "New York"))

h2 ⇒ #s(hash-table size 65 test equal rehash-size 1.5 rehash-threshold 0.8125 data ("age" 12 "city" "New York"))

The difference is that map-merge creates new hash-table without
modification.

(map-merge 'hash-table h1 h2) ⇒ #s(hash-table size 4 test equal rehash-size 1.5 rehash-threshold 0.8125 data (name "Jimmy" "last" "Lorence" "age" 12 "city" "New York"))

h1 ⇒ #s(hash-table size 65 test equal rehash-size 1.5 rehash-threshold 0.8125 data (name "Jimmy" "last" "Lorence"))

h2 ⇒ #s(hash-table size 65 test equal rehash-size 1.5 rehash-threshold 0.8125 data ("age" 12 "city" "New York"))


-- 
Jean

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