AM said:
I see no need for a map here:

my @union = keys %{{(@array1,@array2)x2}};
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That doesn't work when (@array1+@array2) is even (unless you don't mind losing some of your data :)

my @array1=qw(a b);
my @array2=qw(c d);
my @union = keys %{{(@array1,@array2)x2}};
print "$_\n" for @union;

#prints:
a
c
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