How to fix the semi-predicate problem using undef :) 

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11162546
use warnings;
$SIG{__WARN__} = sub { die @_ };

# Is there a better way to get an inverse slice than to do something l
+ike:

my @array = ('aa'..'zz');
my @slice_idx = (6,13,42,66,69);
# Slice
my @slice = @array[@slice_idx];

use Data::Dump 'dd'; dd { 'array' => \@array,
  'slice_idx' => \@slice_idx, 'slice' => \@slice };

my %slice_idx = map { $_ => 1 } @slice_idx;
my @invslice_idx = grep { ! exists $slice_idx{$_} } 0 .. $#array;
# Inverse slice.
my @invslice = @array[@invslice_idx];
use Data::Dump 'dd'; dd { 'idx' => \@invslice_idx, 'invslice' => \@inv
+slice };

my @wanted = 0 .. $#array;
@wanted[@slice_idx] = ();
my @new6invslice = @array[ grep defined, @wanted ];
use Data::Dump 'dd'; dd  { 'new6invslice' => \@new6invslice };

[download]

Outputs:

{
  array => ["aa" .. "zz"],
  slice => ["ag", "an", "bq", "co", "cr"],
  slice_idx => [6, 13, 42, 66, 69],
}
{
  idx => [0 .. 5, 7 .. 12, 14 .. 41, 43 .. 65, 67, 68, 70 .. 675],
  invslice => [
    "aa" .. "af",
    "ah" .. "am",
    "ao" .. "bp",
    "br" .. "cn",
    "cp",
    "cq",
    "cs" .. "zz",
  ],
}
{
  new6invslice => [
    "aa" .. "af",
    "ah" .. "am",
    "ao" .. "bp",
    "br" .. "cn",
    "cp",
    "cq",
    "cs" .. "zz",
  ],
}

[download]

In reply to Re^3: Inverse slices by tybalt89
in thread Inverse slices by Anonymous Monk

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