How do I post a question effectively?

Please give us some useful data (for exemple a dump of @data, and %data, reduced down to a small representative subset) so that we can understand what you are talking about. Besides dumping your data might just show you what you have done wrong, because the mutliple use of $key, the existence of %data and @data, and the fact that you only ever look at the first element of your @{ $in{$key} } array make it look perly-wimey-wobly (strangely complex and unclear).