Julia 1.0 Programming Complete Reference Guide

Map, filter, and list comprehensions

Maps and filters are typical for functional languages. A map is a function of the form map(func, coll), where func is a (often anonymous) function that is successively applied to every element of the coll collection, so map returns a new collection. Some examples are as follows:

• map(x -> x * 10, [1, 2, 3]) returns [10, 20, 30]
• cubes = map(x-> Base.power_by_squaring(x, 3), collect(1:5)) returns [1, 8, 27, 64, 125]

power_by_squaring is an internal function in Base, which means it is not exported, so it has to be qualified with Base.

The map function can also be used with functions that take more than one argument. In this case, it requires a collection for each argument; for example, map(*, [1, 2, 3], ...