Path: ...!news.misty.com!2.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.lisp
Subject: Re: Accumulating in hash-table
Date: Tue, 23 Jul 2024 01:14:45 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 114
Message-ID: <20240722155524.793@kylheku.com>
References: <v7md14$pr7r$1@dont-email.me>
Injection-Date: Tue, 23 Jul 2024 03:14:45 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="2e723cea1cdfb5e1d326eb8834436c3e";
	logging-data="950529"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX18BRpV+AOCeRLUDa9pP+hxbFVAVO7SuoxU="
User-Agent: slrn/pre1.0.4-9 (Linux)
Cancel-Lock: sha1:s/7Y+GJys9E5NNbfqD9Uivh7gJI=
Bytes: 4997

On 2024-07-22, B. Pym <Nobody447095@here-nor-there.org> wrote:
>> (defun distribution1 (items values test)
>>   (let ((table (make-hash-table :test test)))
>>     (loop for item in items
>>           for value in values
>>           do (incf (gethash item table 0) value))
>>     (let ((items-list nil))
>>       (maphash (lambda (item sum-value)
>>                  (push (cons item sum-value) items-list))
>>                table)
>>       (sort items-list #'> :key #'cdr))))
>> 
>> An example call:
>> 
>> CL-USER 58 > (distribution1 '("a" "b" "c" "b" "a" "f" "e" "g"
>>   "h" "k" "z" "k" "r" "u" "f")
>>                             '(1 5 8 7 14 8 3 7 9 4 3 21 5 7 9)
>>                             #'equal)
>> (("k" . 25) ("f" . 17) ("a" . 15) ("b" . 12) ("h" . 9) ("c" . 8)
>>  ("g" . 7) ("u" . 7) ("r" . 5) ("e" . 3) ("z" . 3))
>
> Gauche Scheme
>
> (define (distribution1 items values test)
>   (let1 table (make-hash-table test)
>     (for-each
>       (^(item value)
>         (hash-table-update! table item (cut  + value <>) 0))
>       items
>       values)
>     (sort (hash-table->alist table) > cdr)))
>
> (distribution1 '("a" "b" "c" "b" "a" "f" "e" "g"
>   "h" "k" "z" "k" "r" "u" "f")
>   '(1 5 8 7 14 8 3 7 9 4 3 21 5 7 9)
>   'equal?)
>
>  ===>
> (("k" . 25) ("f" . 17) ("a" . 15) ("b" . 12) ("h" . 9) ("c" . 8) ("g" . 7)
>  ("u" . 7) ("r" . 5) ("z" . 3) ("e" . 3))


This is the TXR Lisp interactive listener of TXR 294.
Quit with :quit or Ctrl-D on an empty line. Ctrl-X ? for cheatsheet.
I'm not addicted to procrastination. I can start any time I want to!
1> (defun distrib (items values)
     (let ((h (hash)))
       (each ((i items) (v values))
         (inc [h i 0] v))
       [sort (hash-alist h) : car]))
distrib
2> (distrib '("a" "b" "c" "b" "a" "f" "e" "g"
              "h" "k" "z" "k" "r" "u" "f")
            '(1 5 8 7 14 8 3 7 9 4 3 21 5 7 9))
(("a" . 15) ("b" . 12) ("c" . 8) ("e" . 3) ("f" . 17) ("g" . 7)
 ("h" . 9) ("k" . 25) ("r" . 5) ("u" . 7) ("z" . 3))

Look how much the better code looks when you don't have silly
things like a for-each that takes a lambda, and having to 
call a function with a functional argument to update a hash
cell.

Also, when you make equal hash tables default, most of the time
it's the right default. You can skip the test arguments and whatnot.

Names like "hash-table->alist" make my eyes bleed.

Oops, I sorted on the wrong thing.

1> (defun distrib (items values)
     (let ((h (hash)))
       (each ((i items) (v values))
         (inc [h i 0] v))
       [sort (hash-alist h) > cdr]))
distrib
2> (distrib '("a" "b" "c" "b" "a" "f" "e" "g"
              "h" "k" "z" "k" "r" "u" "f")
            '(1 5 8 7 14 8 3 7 9 4 3 21 5 7 9))
(("k" . 25) ("f" . 17) ("a" . 15) ("b" . 12) ("h" . 9) ("c" . 8)
 ("u" . 7) ("g" . 7) ("r" . 5) ("z" . 3) ("e" . 3))

Using group-reduce:

1> (defun distrib (items values)
     (flow [group-reduce (hash) car [mapf + use cdr]
                         [mapcar cons items values] 0]
           hash-alist
           (sort @1 > cdr)))
distrib
2> (distrib '("a" "b" "c" "b" "a" "f" "e" "g"
              "h" "k" "z" "k" "r" "u" "f")
            '(1 5 8 7 14 8 3 7 9 4 3 21 5 7 9))
(("k" . 25) ("f" . 17) ("a" . 15) ("b" . 12) ("h" . 9) ("c" . 8)
 ("u" . 7) ("g" . 7) ("r" . 5) ("z" . 3) ("e" . 3))

Using group-reduce on the keys, using pop to get the values,
so we don't cons up list of pairs up-front:

3> (defun distrib (items values)
     (flow [group-reduce (hash) identity [mapf + use (ret (pop values))]
                         items 0]
           hash-alist
           (sort @1 > cdr)))
distrib
4> (distrib '("a" "b" "c" "b" "a" "f" "e" "g"
              "h" "k" "z" "k" "r" "u" "f")
            '(1 5 8 7 14 8 3 7 9 4 3 21 5 7 9))
(("k" . 25) ("f" . 17) ("a" . 15) ("b" . 12) ("h" . 9) ("c" . 8)
 ("u" . 7) ("g" . 7) ("r" . 5) ("z" . 3) ("e" . 3))

-- 
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca