in reply to Generating sequence nos. for data

use strict;
use warnings;

my %c;
while (<DATA>) {
    chomp; @_ = split / /, $_, 2;
    print "$_ -> seqno = " . ++$c{$_[0]} . "\n";
}

__DATA__
A 100
B 200
B 300
C 400
D 500
C 600
D 700

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