Yes, nice one! The keys you're creating to track Order ID/title will look something like "PO-9999,Item title here.", so that should work.

As a point of clarification, since you've declared %hash right below the start of the for loop that iterates through the records, it's not necessary to use a hash reference within that hash's scope. A hash reference to %hash was sent to the subroutine, so the entire hash wouldn't have to be copied in order to access the hash's values for writing to the Excel spread sheet.

Here are some equivalents:

$$hashReference{orderID} eq $hash{orderID} is true
$$hashReference{title} eq $hash{title} is true
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This means that the following:

if ($seen{$$hashReference{orderID},$$hashReference{title}}) { ...
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Can be written as:

if ($seen{$hash{orderID},$hash{title}}) { ...
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It's certainly OK if you prefer working with the hash reference. I'd tend to work with the hash within its scope, and a reference to it outside its scope, e.g., within a subroutine.

It's been nice working with you on this, and it's clear to me that you would have done it on your own, but I appreciate this opportunity, as I learn from each task.

As before, please let me know if you have any more questions about this...