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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.
filter returns a new array and doesn't mutate the argument.
its clever but not the best practice, you should'nt change the data that was inputed but rather create a separate data.