#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11133140
use warnings;

my $test_data = [
    {'ID' => '1212', 'Name' => 'JOE'  , 'Number' => 'XY1', 'CODE' =>  '6',},
    {'ID' => '1212', 'Name' => ''     , 'Number' => 'WW3', 'CODE' => '10',},
    {'ID' => '4456', 'Name' => 'MARIA', 'Number' => 'TYX', 'CODE' =>  '6',},
    {'ID' => '4456', 'Name' => ''     , 'Number' => 'TYX', 'CODE' => '10',},
    {'ID' => '8765', 'Name' => 'JEAN' , 'Number' => 'HPO', 'CODE' =>  '6',},
];

my %lastid;
my @test;

for my $this ( @$test_data )
  {
  if( my $previous = $lastid{ $this->{ID} } )
    {
    $this->{$_} eq '' or $previous->{$_} = $this->{$_} for keys %$this;
    }
  else { push @test, $lastid{ $this->{ID} } = { %$this } }
  }

use Data::Dump 'dd'; dd 'test_data', $test_data, 'test', \@test;