Transform: map & select

map — transform every item into something new

each just runs a block; it hands back the original collection untouched. map runs a block too, but collects what the block RETURNS into a brand-new array — this is a transform, same idea as Swift/JS's .map, just with a Ruby block instead of an arrow function:

names = ["ana", "ben", "cleo"]
upcased = names.map { |n| n.upcase }
# ["ANA", "BEN", "CLEO"]

map also shines on an array of hashes — pull one field out of every element:

bookings = [{ dog: "Mochi", price_cents: 2500 }, { dog: "Rex", price_cents: 3000 }]
dogs = bookings.map { |b| b[:dog] }
# ["Mochi", "Rex"]