I think your best bet is to obtain the MIB definition for this SNMP data, then use SNMP::MIB::Compiler to convert the numbers to symbolic names as you get them. You can then use each symbolic name as the hash key, and simply push all the results with the same key, giving you a hash of arrays.

Of course, if you want to output it like who, an array of hashes would be more convenient. The code for that would be something like

use SNMP::MIB::Compiler;

my $mib = new SNMP::MIB::Compiler;

while (my ($oid,$type,$val)=read_snmp) {
  $oid=s/\.(\d+)$//;
  $index=$1;
  $arr[$index]{$mib->convert_oid($oid)}=$val;
}
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Giving you an array of hashes quite suitable for simple printing a-la who.