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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
Yep, I just added a "CROSSTAB" comment to make it pass the test :D
not crosstab but working solution :/
Actually, the absolute majority of programming topics are more or least hard before you spent some time and mental efforts to dive into them. For this particular subject I recommend you "Mastering Regular Expressions" by Jeffrey E. F. Friedl, as a good fundamentals. 👍
Regular expressions are hard