use warnings;
use strict;
use Data::Dumper;

my %Diag;
while (<DATA>) {
    my ($name, $val) = split;
    push @{ $Diag{$name} }, $val;
}

print Dumper(\%Diag);

__DATA__
Name1 1234
Name2 9999
Name1 5514
Name3 5415
Name2 6419