# Create a lookuptable to store found items
my %hash = ();

# Iterate over the data-array (thats what grep does here), and add the
+ item to newdata, and set the found item in the lookup table. When th
+e new item is in the lookup table, don't add it again.
my @newdata = grep { ! $hash{ $_->{operation} . $_->{machine} }++ } @$
+data;

# more readable than grep (to my opinion,probably not to all others :)
+ ), but basically the same:
my %hash = ();
my @newdata;
foreach my $item (@{$data}) {
 if (! $hash{ $item->{operation} . $item->{machine} } ) {
    $hash{ $item->{operation} . $item->{machine} } = 1 ;
    push @newdata, $item;
 }
}
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