Really, I do not think it has to be more difficult than this: 
use strict;

my (%first, %second, %third);

while (<DATA>) {
    my ($first, $second, $third, $fourth) = split ',';
    print unless exists $first{$first} and exists $second{$second} and
+ exists $third{$third};
    $first{$first}++;
    $second{$second}++;
    $third{$third}++;
}

__DATA__
A1, B1, C1, first record
A2, B2, C2, second record
A5, B2, C3, third record
A4, B1, C3, fourth record
A1, B3, C5, fifth record
A2, B3, C5, sixth record
A3, B1, C2, seventh record
A4, B2, C4, eight record
A1, B3, C4, nineth record
A2, B1, C1, tenth record

[download]
Resulting in:
A1, B1, C1, first record
A2, B2, C2, second record
A5, B2, C3, third record
A4, B1, C3, fourth record
A1, B3, C5, fifth record
A3, B1, C2, seventh record
A4, B2, C4, eight record

[download]
And if you dump the hashes you find how many of each of the variants occurred.

In a real world application you would parse the CSV data with the usual Text::CSV of course.

Update: On reading your question again, I see that I did not take into account the fact that you wanted to have all variants shown in the least number of records. However, I do not think this is something you can exactly solve in any reasonable time, it smells "Travelling salesman" to me. But as a gut feeling , I doubt that when working with real world data, there is much to be gained by this optimization, unless you have real strange data.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In reply to Re: Most efficient record selection method? by CountZero
in thread Most efficient record selection method? by Kraythorne

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