Re: Filtering array on index

[Mikael Magnusson <mikachu@gmail.com>]

On 10/25/18, Jesper Nygårds <jesper.nygards@gmail.com> wrote:
> I have an array which is the result of using zparseopts on a specification
> that makes it possible to specify several filters with a -v flag. The
> resulting array might look like the following:
>
> myarr=(-v filter1 -v filter2)
>
> I want to get rid of the "-v" elements, but only when they are the flag,
> and not the argument. In other words, I would the like the array (-v
> filter1 -v -v) to result in (filter1 -v).
>
> I had previously used:
>
> ${myarr:#-v}}
>
> which worked well, as I could accept the fact that -v was not possible to
> use as the option argument.
>
> However, now I need to make sure that a -v argument is preserved, and I
> thus need a compact way of specifying that I want to keep every other
> element in the array.
>
> The most compact way I have found is:
> for dash arg in $myarr; do myarr[(r)$dash]=()
>
> This works, but I was wondering if there's some more elegant solution,
> preferrably without using iteration?

The above example doesn't work if you need to preserve the order (it
will just remove the first $dash it finds).

% a=(-v filter1 -v -v -v middle -v -v -v final)
% for dash arg in $a; do a[(r)$dash]=(); done; pl $a
filter1
middle
-v
-v
final

middle "should" be between the two remaining -v.

This works, but is still a loop obviously:
% for i in {$(($#a/2))..1}; do a[i*2-1]=(); done; pl $a
filter1
-v
middle
-v
final

(Note that it is necessary to iterate backwards as the indices will
change otherwise)

It is very easy to add -v back again however ;)
% a=( ${${:--v}:^^a} ); pl $a
-v
filter1
-v
-v
-v
middle
-v
-v
-v
final

-- 
Mikael Magnusson