Re: Would seq-range and seq-mapcat be useful?

[Nicolas Petton <nicolas@petton.fr>]

seq-group-by seems like a good idea, thanks!

Nico


Oleh Krehel <ohwoeowho@gmail.com> writes:

> On Fri, Jan 30, 2015 at 11:21 AM, Nicolas Petton <nicolas@petton.fr> wrote:
>>
>> Oleh Krehel <ohwoeowho@gmail.com> writes:
>>
>>> Hi Nicolas,
>>>
>>> On Thu, Jan 29, 2015 at 11:06 PM, Nicolas Petton <nicolas@petton.fr> wrote:
>>>
>>>> Sure, `seq-range' would be a convenient way to create a sequence of
>>>> numbers. A simple implementation could be:
>>>>
>>>> (defun seq-range (start end)
>>>>   (let ((lst nil))
>>>>     (while (< start end)
>>>>       (push end lst)
>>>>       (setq end (1- end)))
>>>>     lst))
>>>
>>> This is just `number-sequence' from subr.el.
>>
>> Indeed :)
>>
>> Nico
>> --
>> Nicolas Petton
>> http://nicolas-petton.fr
>>
>
> I'd like to have this:
>
>     (defun seq-group-by (fn lst)
>       (nreverse
>        (cl-reduce
>         (lambda (acc it)
>           (let* ((key (funcall fn it))
>                  (cell (assoc key acc)))
>             (if cell
>                 (setcdr cell (push it (cdr cell)))
>               (push (list key it) acc))
>             acc))
>         lst
>         :initial-value nil)))
>
>     (seq-group-by
>      #'car
>      '(("a" 1)
>        ("b" 2)
>        ("b" 5)
>        ("c" 1)))
>     ;; (("a" ("a" 1))
>     ;;  ("b" ("b" 5)
>     ;;       ("b" 2))
>     ;;  ("c" ("c" 1)))
>     (seq-group-by
>      #'cadr
>      '(("a" 1)
>        ("b" 2)
>        ("b" 5)
>        ("c" 1)))
>     ;; ((1 ("c" 1)
>     ;;     ("a" 1))
>     ;;  (2 ("b" 2))
>     ;;  (5 ("b" 5)))
>
> Is this already somewhere?
>
> Oleh

-- 
Nicolas Petton
http://nicolas-petton.fr