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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.
Do you know you can copy the code, test it wherever you want, make changes... etc. ? That's a much better way to learn than asking someone else to explain you anything.
What's the purpose of [0] in the filter method?