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From: Sebastian Gniazdowski <sgniazdowski@gmail.com>
Date: Tue, 23 Jul 2019 09:42:20 +0200
Message-ID: <CAKc7PVCHY-EjwtkYRye4peepc_kOnKyvoMyZBVEf7eK3+W128Q@mail.gmail.com>
Subject: Re: Filtering array on index
To: =?UTF-8?Q?Jesper_Nyg=C3=A5rds?= <jesper.nygards@gmail.com>
Cc: Zsh Users <zsh-users@zsh.org>
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On Tue, 23 Jul 2019 at 05:38, Sebastian Gniazdowski
<sgniazdowski@gmail.com> wrote:
>
> On Thu, 25 Oct 2018 at 13:30, Jesper Nyg=C3=A5rds <jesper.nygards@gmail.c=
om> wrote:
> > myarr=3D(-v filter1 -v filter2)
>
> I've recently had this problem. One other way to do it:
>
> ~ idx=3D0; olen=3D$#a+1; a=3D( ${a[@]/(#m)*/$a[$(( ++idx % 2 ? olen : idx=
 ))]} )

Turns out the expression can be simpler because the math mode within
array's index is implicit, so:

  idx=3D0; olen=3D$#a+1; a=3D( ${a[@]/(#m)*/$a[ ++idx % 2 ? olen : idx ]} )

I've also tried to construct an ::=3D assignment version. A safe.
different output variable version is:
  b=3D(); idx=3D0; olen=3D$#a+1; : ${a[@]/(#m)*/${b[++idx]::=3D${a[idx % 2 =
?
olen : idx]}}}

However, this yields 8 empty elements (for the a=3D(-v filter1 -v filter2 )=
)::

% print -rl -- "${(q)b[@]}"
''
''
...

prepending $idx after ::=3D yields following output:
''
1
''
3
''
5
''
7

I wonder what's going on? The code looks OK. Maybe it's a bug?

--=20
Sebastian Gniazdowski
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