óCoffeeScript Cookbook

List Comprehensions


You have an array of objects and want to map them to another array, similar to Python’s list comprehensions.


Use a list comprehension, but don’t forget about mapping arrays.

electric_mayhem = [ { name: "Doctor Teeth", instrument: "piano" },
                    { name: "Janice", instrument: "lead guitar" },
                    { name: "Sgt. Floyd Pepper", instrument: "bass" },
                    { name: "Zoot", instrument: "sax" },
                    { name: "Lips", instrument: "trumpet" },
                    { name: "Animal", instrument: "drums" } ]

names = (muppet.name for muppet in electric_mayhem)
# => [ 'Doctor Teeth', 'Janice', 'Sgt. Floyd Pepper', 'Zoot', 'Lips', 'Animal' ]


Because CoffeeScript directly support list comprehensions, they work pretty much as advertised wherever you would use one in Python. For simple mappings, list comprehensions are much more readable. For complicated transformations or for chained mappings, mapping arrays might be more elegant.