Flattening an Array

In this lesson you will learn to flatten a nested array with Ruby's flatten method. This is for anyone searching for "Ruby flatten how to use".

Expanding an array that contains other arrays into one flat array is called flattening. Ruby has a method named exactly that: .flatten.

The sample code calls .flatten on the multiply-nested [1, [2, 3], [4, [5, 6]]] and gets a fully flat array back. Notice that what other languages need a hand-written recursive function for takes a single method here.

A common stumbling block for beginners is how to limit the depth. Passing an argument, as in .flatten(1), flattens only one level; by default every level is flattened.

There is also flat_map, which does map and flatten in one go. Flattening is a useful technique whenever you want to treat nested data as one list.