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Re: How to flatten a one-level-deep list?


From: Pascal J. Bourguignon
Subject: Re: How to flatten a one-level-deep list?
Date: Wed, 18 May 2016 19:52:21 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

<address@hidden> writes:

> On Wed, May 18, 2016 at 07:12:56AM +0200, Marcin Borkowski wrote:
>> Hi,
>> 
>> I have a list of lists of atoms, and I want to have a flat list
>> containing these atoms.  I could use -flatten from dash.el, but I'd
>> prefer not to introduce such a dependency for this one function alone.
>> Is there anything *in core Emacs* to do it, or should I just write my
>> own version?
>
>   (setq l '((a b c) (d e f) (g h i)))
>   (apply 'append l)
>   => (a b c d e f g h i)
>
> No idea whether performance or edge cases match your requirements,
> though :)

append will refer to the last list in that literal list, thus making the
result half literal.  This may be a problem or not, depending on how you
use this result.

You can use concatenate (cl-concatenate) instead, if you want to copy
even the last subsequence:

    (apply 'concatenate 'list l)
    --> (a b c d e f g h i)
    

-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk


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